DE102013109276A1 - Apparatus and method for identifying a modulation method used for a symbol transmitted over a selected subcarrier - Google Patents

Abstract

Embodiments relate to a device (100) for identifying a modulation method used for a symbol (92) transmitted over a selected subcarrier, based on a received OFDM signal (96) comprising a plurality of subcarriers (90; 94a-94c). The apparatus comprises a classifier (110) configured to determine at least one reception parameter characterizing a plurality of subcarriers (90; 94a-94c); and an evaluator (120) configured to determine, for each modulation method of a plurality of possible modulation methods, a usage probability using the reception parameter. An identifier (130) is arranged to identify the modulation method used as the modulation method of the plurality of possible modulation methods that corresponds to the highest probability of use.

Description

Embodiments are concerned with a method and apparatus for identifying a modulation method used on the transmitter side to modulate a symbol transmitted over a selected subcarrier.

Applications in which the modulation methods for generating transmitted symbols are varied depending on the instantaneous quality of a transmission channel between a transmitter and a receiver are diverse. This adaptive modulation is a method to efficiently utilize the channel capacity of a time-varying multipath transmission channel, for example, in an Orthogonal Frequency Domain Multiplexing (OFDM) transmission system. For this purpose, the modulation methods are adapted to the current state of the transmission channel. The aim is to use more spectrally efficient modulation techniques on those subcarriers of a multi-subcarrier OFDM signal having higher channel quality while using simpler, more robust modulation schemes on lower quality subcarriers. This can lead to an improvement in the performance or the efficiency of the overall system, which, for example, with a bit error probability of 10 ^-3 and constant data rate, can allow a reduction of the transmission power between 5 and 15 dB compared to a system with fixed modulation. In order to enable the receiver to correctly demodulate the signal, the information about the modulation methods used is conventionally transmitted from the transmitter to the receiver, ie the receiver is informed on which subcarrier or for which symbol which modulation method was used in order to demodulate it Able to correctly detect the contents of the symbol. Usually, this information is explicitly signaled by control bits or control information, which can lead to a partial considerable reduction in the bandwidth efficiency, ie the payload transmissible per bandwidth. One approach to prevent this is to enable the receiver to independently identify the modulation method itself by means of an automatic modulation classification.

One way to conclude the modulation used in a subcarrier for the currently received symbol, for example, is to maximize the likelihood function that a specific modulation was originally used for an actually received point in the constellation diagram. This probability is based on a sum of exponential functions, the sum having a number of summands corresponding to the number of constellation points of the modulation method. The exponents each have a term that corresponds to the distance of the received symbol from one of the possible constellation points. Therefore, in this approach, for each modulation type, depending on its order or possible points in the constellation diagram, a plurality of partially complex calculations are performed. This can cause the method to be inapplicable in systems that communicate approximately in real time. Reasons can be that the necessary calculations take too long or that on the receiving device, such as a mobile phone or any wireless communication device necessary for pursuing this approach computing capacity is not available.

Another way to deduce the modulation used is feature-based methods or approaches. In these feature-based methods, a set of features is extracted from the signal that may be characteristic of the modulation used to generate the received signal. Based on the extracted features, the assignment then takes place to the estimated modulation used. Although this method may possibly be implemented more computationally efficient than the probabilistic approach, the reliability with which the modulation actually used is determined is typically even less than that due to the fact that feature-based methods use only a portion of the information available probabilistic approach. Furthermore, feature-based methods have the disadvantage that they function only to a limited extent in modulation methods of the same class because of the then similar features. Both of the methods use only the received signal of a subcarrier for the classification in order to estimate the modulation on the relevant subcarrier. This requires that the signal may have to be monitored for a long time or for several successive frames of an OFDM signal in order to obtain a comparatively reliable statement about the modulation method used, despite considerable computing capacity.

This in turn reduces applicability in real-time applications where low latencies are required. In the case of OFDM systems, for example, the length of an OFDM frame additionally becomes possible due to possible synchronization errors and channel estimation errors due to the temporally variable ones Channels limited so that a short frame length or observation time can result. Examples of such applications are WLAN networks, in particular a WLAN client, a laptop, a mobile telephone, a measured value recorder or the like, as well as all possible unidirectional or bidirectional communication systems, which can assign contents to be transmitted to symbols of different modulation levels, the efficiency of the transmission to increase.

Specific implementations of the likelihood-based modulation classification are, for example, in the Chinese patent application CN202918327U , as well as in the US patent applications US2006115013A . US8358723B described.

Examples of implementations of the feature-based modulation classification can be found inter alia in the Korean patent application KR20070000274A in the US patent application US2006072679A and in the French patent application FR2713799A ,

Thus, in view of the hitherto proposed methods of identifying a modulation method used for a symbol transmitted over a selected subcarrier, there is a need to reduce the time it takes to identify a used modulation with a certain probability of error, e.g. Possibility to use automatic modulation classification in real-time communication systems.

Embodiments make this possible by determining, in a method for identifying a modulation method used for a symbol transmitted over a selected subcarrier, which is based on a received OFDM signal comprising a plurality of subcarriers, a reception parameter jointly characterizing at least a plurality of subcarriers. Using the reception parameter, a usage probability can then be determined for each modulation method of a plurality of possible modulation methods. Based on the usage probabilities for the individual modulation methods, the modulation method is identified as probably used, which leads to the highest probability of use or corresponds to the highest probability of use.

By using the reception parameter, which characterizes a plurality of subcarriers together, the number of symbols used for the classification and the observation time of the received signal can be reduced, so that by means of some embodiments a classification with a low probability of error can be achieved within a shorter period of time which allows the application of some embodiments in real bi-directional communication systems.

According to some embodiments, the receive parameter is a first order statistical parameter that characterizes a plurality of estimated channel coefficients, each of the channel coefficients characterizing a subcarrier and indicating an estimated transmission behavior of the transmission channel corresponding to the respective subcarrier between the sender and the receiver. That is, a plurality of subcarriers are characterized by only one parameter, which in some embodiments reduces the classification error probability without causing high additional computational load, so that such embodiments may also be used on mobile computing devices with limited computing power.

The use of the reception parameter characterizing the plurality of subcarriers can, for example, take account of the fact that the transmitter also takes into account the quality of the channels of further subcarriers in deciding which modulation method is used for a specific subcarrier. This will be explained in more detail below with reference to the specific embodiments.

For example, according to some embodiments, the first-order static parameter may be the mean of the squares of the estimated channel coefficients.

In accordance with some further embodiments, in determining the usage probability, another second order statistical parameter is used for the plurality of channel coefficients. In some embodiments, with only a moderate increase in the computational load, this can lead to the classification with a certain error probability occurring even faster, or the achievable error probability can be further reduced.

According to some embodiments, the quadratic deviation of the squares of the estimated channel coefficients from their mean value is used as a further reception parameter.

According to some embodiments, when determining the probability of use, a probability is taken into account to obtain the actually estimated channel coefficient for the subcarrier under consideration at the currently determined reception parameter. That is to say, information is additionally evaluated which indicates the probability of obtaining a specific channel characteristic for the specific characteristic of the plurality of subcarriers for a specific subcarrier. This conditional probability may increase the classification accuracy in some embodiments.

According to some other embodiments, for similar reasons, a second conditional probability is taken into account to use a particular modulation method of the plurality of possible modulation methods for the subcarrier currently considered, if the plurality of subcarriers have a characteristic that corresponds to the particular reception parameter.

According to further embodiments, the determination of the probability of use further takes into account a third probability which contains only information about the considered subcarrier and which indicates the probability of having a received symbol or a particular modulation method at the particular channel coefficient. to get the constellation point received in the constellation diagram.

According to some other embodiments, this third probability, which is similar in character to the likelihood functions, is determined by approximating the natural logarithm of the likelihood function, which according to some embodiments may result in a significant reduction in computational capacity.

According to some embodiments, the method or apparatus is used in a Time Division Duplex (TDD) OFDM signal, which, according to some embodiments, may allow to approximate the channel coefficients used on the sender side for automatic allocation to make the modulation.

Exemplary embodiments are explained in more detail below with reference to the accompanying figures. Show it:

1 an embodiment of an apparatus for identifying a modulation method used for a symbol transmitted over a selected subcarrier;

2 an illustration of an OFDM signal or an OFDM frame;

3 the distribution of constellation points for five different modulation methods;

4 a constellation diagram of the 4 QAM modulation illustrating the approximate calculation of the likelihood function for the 4 QAM modulation;

5 a constellation diagram of the 16 QAM modulation illustrating the approximate calculation of the likelihood function for the 16 QAM modulation;

6 a schematic illustration of a TDD-OFDM system;

7 an alternative schematic illustration of an embodiment of an apparatus for identifying a used modulation method; and

8th a flow chart of an embodiment of a method.

Various embodiments will now be described in more detail with reference to the accompanying drawings, in which some embodiments are illustrated. In the figures, the thickness dimensions of lines, layers and / or regions may be exaggerated for the sake of clarity.

In the following description of the attached figures, which show only some exemplary embodiments, like reference characters may designate the same or similar components. Further, summary reference numerals may be used for components and objects that occur multiple times in one embodiment or in a drawing but are described together in terms of one or more features. Components or objects which are described by the same or by the same reference numerals may be identical in terms of individual, several or all features, for example their dimensions, but may also be different if the description does not explicitly or implicitly make reference to the description.

Although embodiments may be modified and changed in various ways, exemplary embodiments are illustrated in the figures as examples and will be described in detail herein. It should be understood, however, that it is not intended to limit embodiments to the particular forms disclosed, but that embodiments are intended to cover all functional and / or structural modifications, equivalents and alternatives that are within the scope of the invention. Like reference numerals designate like or similar elements throughout the description of the figures.

Note that an element referred to as being "connected" or "coupled" to another element may be directly connected or coupled to the other element, or intervening elements may be present. Conversely, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other terms used to describe the relationship between elements should be interpreted in a similar manner (eg, "between" versus "directly in between," "adjacent" versus "directly adjacent," etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments. As used herein, the singular forms "a," "a," "an," and "the" are also meant to include the plural forms unless the context clearly indicates otherwise. It should also be made clear that the terms such. "Including," "including," "and / or having," as used herein, indicates the presence of said features, integers, steps, operations, elements, and / or components, but the presence or addition of one or more features, integers, steps, operations, elements, components and / or groups thereof.

Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning as commonly assigned to one of ordinary skill in the art to which the embodiments pertain. Furthermore, it should be clarified that expressions, e.g. For example, those defined in commonly used dictionaries are to be interpreted as having the meaning consistent with their meaning in the context of the relevant art and not to be interpreted in an idealized or overly formal sense, as long as this is so not expressly defined herein.

By way of example with reference to the following figures, for a time-division duplex-based OFDM system with N-subcarriers through which data are transmitted, one possible implementation of a device or a method for identifying a symbol transmitted over a selected subcarrier described r _n used modulation method. For this purpose, it is assumed that the classification or the exemplary embodiment is implemented on a receiver, for example on a mobile device, it being understood that further exemplary embodiments can also be used on the side of a base station. In the system considered by way of example, a total of five modulation methods can be used as a plurality of possible modulation methods whose constellation diagrams are included for the sake of completeness 3 are shown. The first constellation diagram 10 Corresponds to the state NoTx (no modulation, 0 bit), the second constellation diagram 20 to BPSK (Binary Phase Shift Keying, 1 bit), the third constellation diagram 30 to 4-QAM or QPSK (Quadrature Phase Shift Keying, 2 bits). The fourth constellation diagram 40 corresponds to 16-QAM (4 bits) and the fifth constellation diagram 50 shows the constellation points for 64-QAM (6-bit) modulation.

The embodiments use a receive parameter characterizing a plurality of subcarriers to identify a modulation used, taking into account the fact that a plurality of subcarriers are also considered at the transmitter end in order to decide which modulation is used on a specific subcarrier. For example, at the transmitter, the decision may be made based on two pieces of information, namely on an estimated channel vector the last uplink direction H ^{U of} the base station and at the currently used data rate, resulting in a number of bits B to be transmitted in an OFDM symbol. The data rate can be specified externally, for example, or varied channel-adaptively, as is the case for example in cordless network systems (wireless LAN, WLAN).

• – Eine bestimmte Anzahl von bits B muss in einem OFDM-Symbol geladen werden.
• – Die Bitfehlerwahrscheinlichkeit ist stets zu minimieren.

For a given data rate, adapting the modulation scheme for each subcarrier corresponds to adaptive bit loading performed by a sender. On each of the plurality of subcarriers, a predetermined number of bits are derived per OFDM symbol, which is derived from the set M = {0, 1, 2, 4, 6}. A bit-loading vector for all N subcarriers is hereinafter referred to as b. Each individual element of b comes from the set M. The sum of all elements is the number of bits B. One possibility of the adaptive distribution of the modulation methods to the respective subcarriers consists in the consideration of the two conditions:

• - A certain number of bits B must be loaded in an OFDM symbol.
• - The bit error probability should always be minimized.

To satisfy these two conditions, the bit load algorithm is iteratively performed. One starts from an initial error probability that is small enough. Each time additional bits are loaded on any subcarrier, the probability of error increases, but the bit loading is designed so that the probability of error is always minimal. This may require an iterative scanning process. In each iteration, only on that subcarrier are so many bits loaded that a minimal increase in the error probability is ensured. This process is repeated until the intended number of bits B is loaded. This means a sub-carrier allocation of bits. The number of bits loaded on a subcarrier thus depends not only on its own channel state, but also on the channel states of all other subcarriers. The channel state is a synonym for the transmission behavior of the physical transmission channel corresponding to the subcarrier considered or used by it. Thus, global minimization of the error probability is possible with the constant number of bits to be loaded.

Some embodiments may, for example in a mobile station, blindly detect the bit-loading vector b. For this purpose you use a receive parameter characterizing a plurality of subcarriers, ie additional information available to the mobile station. The classification may use the received signal vector r _n , the data rate or the number of bits B as well as the estimated uplink channel vector of the base station. The data rate can be made available for example via a control channel of the mobile station, so that some embodiments can integrate this information into the classification algorithm. For slow time varying channels, the estimated uplink channel vector of the base station may be approximated by the estimated downlink vector of the mobile station H ^D. This applies, for example, to a TDD system in which the base station and the mobile station operate on the same frequency band. Thus, some embodiments on mobile stations may also incorporate the estimated downlink vector H ^D into the classification algorithm.

In general, the modulation classification, that is to say the identification of a modulation method used for a symbol r _n transmitted via a selected subcarrier, can be represented mathematically as follows: b (n) / i, MAP = p (b _i | r _n , HD / n, B), where b _{i is} a modulation candidate from the set M = {0, 1, 2, 4, 6} and b (n) / i, MAP represents the classified modulation candidate. Since the modulation classification also uses the a-priori information B and H ^{D in} addition to the received vector r _n of symbols r _n , exemplary embodiments can also be referred to as maximum-a-posteriori-probability (MAP) -based methods and devices. In particular, embodiments use a reception parameter which jointly characterizes a plurality of subcarriers and which can be based, for example, on H ^D.

1 schematically shows an embodiment of a device 100 for identifying one for one over a selected subcarrier 90 transmitted symbol 92 used modulation method based on one of a plurality of subcarriers 90 and 94a to 94c comprehensive receiving OFDM signal 96 , The OFDM signal is in the 1 for the sake of clarity only schematically illustrated, whereas on a more detailed description of an OFDM signal 2 is referenced. The device 100 has a classifier 110 configured to determine a reception parameter characterizing at least a plurality of subcarriers. An evaluator 120 is trained to work for everyone Modulation method of a plurality of possible modulation method to determine a use probability, wherein the respective use probability is determined using the reception parameter. In the present case, the in 3 five modulation methods shown, it being understood that according to further embodiments, a smaller or a larger number of modulation methods may be possible, and thus may correspond to the plurality of possible modulation methods. In particular, these may also include other modulation methods than those in 3 shown.

The identifier 130 is designed to identify the modulation method used as the one modulation method of the plurality of possible modulation methods, which leads to the highest probability of use. That is, the identifier identifies one of the possible modulation methods b _i as used.

2 shows one way in which an OFDM signal can be constructed. The OFDM signal 96 consists of a plurality of subcarriers, with the subcarrier being exemplified for the following discussion 90 is to be considered as the selected subcarrier for which the modulation used for the symbol 92 should be determined. The individual subcarriers of the OFDM signal 96 are arranged in mutually adjacent frequency ranges. Within each subcarrier 90 . 94a -C becomes a symbol generated with a certain modulation method during a symbol duration 98 (t _sym ) transmitted. The in 2 shown OFDM signal frame also begins with a so-called preamble 99 within which a known number of consecutive symbols with a fixed modulation is transmitted in each subcarrier. The pre-preamble previously known to the receiver can, according to some embodiments, be used on the receiver side, for example, for channel coefficients H D / n for each of the subcarriers n which approximate the transmission behavior of the physical channel for each of the subcarriers, for example as an amplitude attenuation value and as a phase factor describing the phase shift of the symbol over the channel.

The preamble is followed by a plurality of successive symbols within each subcarrier whose modulation is not fixed a priori, but whose modulation is varied on the transmitter side, for example, to achieve a lower probability of error during transmission with a given transmission power and data rate than with fixed modulation. In general, the majority of these within a symbol time 98 transmitted symbols are referred to as an OFDM symbol, so that an OFDM symbol thus each comprises a symbol r _n on each of the N subcarriers.

Although, according to the implementations described in more detail below, all N subcarriers of the OFDM signal are used to determine the receive parameter, according to further embodiments only one subset, ie at least a plurality of all subcarriers, may be used to determine the receive parameter for classification.

Before considering a concrete implementation of an embodiment in which two parameters are used to approximately describe the channel states of all subcarriers, it should again be pointed out that further embodiments may only use one reception parameter, which may be one of the following two parameters, for example also a different one.

The channel vector H ^D is assumed to be already estimated below and has the components H D / n , which can be derived for example for each subcarrier n from the preamble. In most practical systems, the vector H ^{D has} a large dimension, for example, at LTE, from 128 to 2048, depending on the bandwidth used. Even at IEEE 802.11a there are still 64 subcarriers, of which 48 subcarriers are used for data transmission. To make the embodiments efficiently implementable, the dimension of H ^{D is} reduced by using a receive parameter characterizing at least a plurality of subcarriers. In the specific embodiment described, two receive parameters are used.

The first reception parameter is given by μ 2 / H = 1 / NΣ N-1 / n = 0 | HD / n | ² and thus describes the average power attenuation through the channel of the OFDM signal.

The second receive parameter is given by σ 2 / H = 1 / NΣ N-1 / n = 0 | HD / n | ² - μ 2 / H) ² and thus describes the dispersion of the channel states of all subcarriers or the strength of the frequency selectivity of the entire channel.

wobei b (n) / i,3–D die klassizifierte Modulation gemäß dem Ausführungsbeispiel ist. In dieser Gleichung tauchen als die Kanalinformation nur H D / n und die oben eingeführten zwei Empfangsparameter auf. So wird die Dimension des Anteils des gesamten Kanals von einer großen Zahl N nun auf 3 reduziert: der Kanalzustand des Subträgers n, dessen Modulation zu klassifizieren ist und die zwei Parameter, die näherungsweise den Effekt der anderen Subträger (subträgerübergreifende adaptive Modulation) beschreiben. So kann man Ausführungsbeispiele auch als 3-D Approximation bezeichnen. If the modulation method on the subcarrier n is now to be classified, embodiments using the above-mentioned dimensional reduction can be represented as follows:

where b (n) / i, 3-D is the classified modulation according to the embodiment. In this equation, as the channel information, only H appears D / n and the above introduced two reception parameters. Thus, the dimension of the proportion of the entire channel from a large number N is now reduced to 3: the channel state of the subcarrier n whose modulation is to be classified and the two parameters which approximately describe the effect of the other subcarriers (subcarrier-adaptive modulation). Thus, embodiments can also be referred to as 3-D approximation.

Although according to the embodiment just described, the classification or identification of the modulation method used for a selected subcarrier based on a single OFDM symbol is possible, according to further embodiments in which within an OFDM frame consisting of K symbols, the Classification also be made in knowledge of all received symbols r _{k, n of} an OFDM frame. That is, the identifier identifies that modulation method b (n) / i, 3-D as the allegedly used, which fulfills the following condition:

This can be particularly possible or even advantageous if only one modulation is used within an OFDM frame for each subcarrier. According to alternative embodiments, in which a plurality of modulation methods are also used within a subcarrier within an OFDM frame, the classification can also be made separately for each individual received symbol.

Using all received symbols of a frame, only the last of the three terms used for classification according to the procedure described above, namely that which depends on the actual received point in the constellation diagram r _{k, n} , changes. The other two terms, which according to the embodiments consider the influence or the information of the other subcarriers, are not changed thereby. In particular, in both implementations discussed herein, the embodiments use a first conditional probability, for the particular receive parameters for the considered subcarrier n, the channel coefficient H D / n appreciate: p (| HD / n || μ 2 / H, σ 2 / H, b _i , B).

Further, both implementations use a second conditional probability in the two particular receive parameters for the considered sub-carriers the modulation method b n I of possible modulation schemes to be used _i the plurality: p (b _i | μ 2 / H, σ 2 / H, B).

Further, according to some embodiments, third likelihood is the likelihood function p (r _n | HD / n, b _i) , ie the probability at which certain channel coefficients H D / n and assuming the modulation symbol b _i via the subcarrier n, the symbol r _{n is} approximated to reduce the complexity of the computation.

exponentiellen Funktionen erforderlich, z. B. bei 16-QAM 2⁴ = 16 exponentielle Funktionen. Bei 64-QAM wären 64 exponentielle Funktionen zu berechnen. Um die Berechnung von exponentiellen Funktionen zu vermeiden, wird gemäß einigen Ausführungsbeispielen eine Approximation eingeführt. Das Prinzip wird anhand des Beispiels von 4-QAM und von 4 erläutert. Dabei werden die folgenden Schritte durchgeführt:
Zunächst wird der Logarithmus der Likelihood-Funktion gebildet. Dies ist erlaubt, weil die logarithmische Funktion eine monoton steigende Funktion ist und der Logarithmus somit keine negativen Auswirkungen für das Bewertungskriterium hat.To evaluate this likelihood function exactly, an evaluation of

exponential functions required, eg. For example, 16-QAM 2 ⁴ = 16 exponential functions. For 64-QAM, 64 exponential functions would have to be calculated. To avoid the computation of exponential functions, an approximation is introduced according to some embodiments. The principle is based on the example of 4-QAM and of 4 explained. The following steps are performed:
First, the logarithm of the likelihood function is formed. This is allowed because the logarithmic function is a monotone increasing function and therefore the logarithm has no negative impact on the evaluation criterion.

In addition, the symmetry property of the quadratic constellation points of 4-QAM is exploited: x ⁽¹⁾ = x ⁽²⁾ = -x ⁽³⁾ = -x ⁽⁴⁾ y ⁽¹⁾ = -y ⁽²⁾ = -y ⁽³⁾ = y ⁽⁴⁾ .

In addition, the following approximation can be exploited:

This allows the original likelihood function to be approximated by the following equation: ln (p (r _{k, n} | HD / n, b _i )) ≈ -ρ 2 / n | x ₍₁₎ + y ₍₁₎ | ² + 2ρ 2 / n [| x _{k, n} x ⁽¹⁾ | + | y _{k, n} y ⁽¹⁾ |] - 2 ln (2).

As can be seen in this equation, the exponential functions are eliminated. There are only additions and multiplications to perform.

This principle can be applied to all symmetrically and quadratically arranged constellation diagrams of other modulation methods. If necessary, an additional coordinate transformation must be carried out for the 4-point approximation, as for the 16-QAM modulation using 5 is illustrated.

The following applies:

With these definitions, the approximate calculation of the five different modulation methods b _i considered here can be stated as follows:

In summary, as a third considered probability, some embodiments use an approximation of the natural logarithm of the likelihood function p (r _n | HD / n, b _i) for square and symmetrically arranged constellation points according to one of the approximations given above.

In addition to the simplification of the calculation described above, the use of the 4-point approximation just described may, in some embodiments, result in subsequent demodulation itself with reduced computational power, if instead of all constellation points only 4 adjacent possible constellation points need to be considered ,

6 schematically shows the application of an embodiment in a time-division-duplex (TDD) system comprising a transmitter 200 and a receiver 300 includes. In a TDD system, both the transmitter 200 as well as from the receiver 300 at different times a transmission of an OFDM signal over the same OFDM channel, ie performed in the same frequency range, but at different times. For example, the transmitter transmits a first OFDM frame in a first transmitter time interval (t-1) 202 , In a subsequent second transmitter time interval (t), the receiver transmits 300 again a second OFDM frame containing a possible response 302 ,

In particular, in a TDD system, as in 6 is shown only schematically, the signal received in the present transmitter time interval can provide a good approximation of the channel estimation of the individual subcarriers that a transmitter 200 based on an OFDM frame received immediately before and on which the adaptive distribution of the modulations of the transmitter 200 for the different subcarriers.

7 again schematically illustrates an embodiment of an apparatus for identifying a modulation method used for a symbol r _n transmitted over a selected subcarrier 140 , In particular, in the schematic representation of 7 illustrates based on what information the embodiment of a device 100 the modulation method used 140 (b _n ) determined. According to some embodiments, the received signal vector becomes 150 (r _n ), an estimated downstream channel vector 160 (H ^D ) and the knowledge about the data rate 170 (B) used to the modulation method 140 to identify.

For the sake of completeness shows 8th again schematically in the form of a flowchart an embodiment of a method for identifying a modulation method used by a subcarrier.

The method includes determining 800 at least one reception parameter E characterizing a plurality of subcarriers, as well as a further determination 810 a usage probability for each modulation method of a plurality of possible modulation methods using the reception parameter E.

The method further includes identifying 820 the modulation method used as the modulation method of the plurality of possible modulation methods, which leads to the highest probability of use or corresponds.

In summary, embodiments use information about a characteristic of a plurality of subcarriers to enable identification of the modulation method used for a selected subcarrier.

This may improve the result, for example, as compared to other methods that operate on a heuristic basis, in which there are no analytical methods for parameter setting, and an extensive search is required to find a meaningful parameter setting, in accordance with some embodiments.

This may further improve the result according to some embodiments, for example, as compared to other methods that use the additional information available for the modulation classification incompletely and in a greatly simplified form. In particular, when the fact of sub-carrier optimization in the adaptive modulation on the transmitting side is not taken into account.

Further, some embodiments may be used even if the transmitter and the receiver do not use the same adaptive modulation technique. This is the case with most practical ones Because not every system uses bilateral adaptive modulation. For example, sometimes a mobile station may not be able to perform the adaptive modulation due to the limited computational power. Even if adaptive modulation is used on both sides, the same adaptive modulation method is usually not used. The two sides may have different system requirements, e.g. For example, the base station may have other requirements to meet than the mobile station, so that the above requirement is not met.

Although the preceding embodiments separately identify the modulation methods for each subcarrier, according to further embodiments it is also possible to identify the modulation method used in common for several subcarriers, if, for example, several subcarriers are considered together at the transmitter side on the transmitter side due to the small frequency spacing in the decision for the modulation method used or combined into a subband in view of this decision.

The features disclosed in the foregoing description, the appended claims and the appended figures may be taken to be and effect both individually and in any combination for the realization of an embodiment in its various forms.

Although some aspects have been described in the context of a device, it will be understood that these aspects also constitute a description of the corresponding method, so that a block or a component of a device is also to be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block or detail or feature of a corresponding device.

Depending on particular implementation requirements, embodiments of the invention may be implemented in hardware or in software. The implementation may be performed using a digital storage medium, such as a floppy disk, a DVD, a Blu-Ray Disc, a CD, a ROM, a PROM, an EPROM, an EEPROM or FLASH memory, a hard disk, or other magnetic disk or optical memory are stored on the electronically readable control signals, which can cooperate with a programmable hardware component or cooperate such that the respective method is performed.

A programmable hardware component may be integrated by a processor, a central processing unit (CPU), a graphics processing unit (GPU), a computer, a computer system, an application-specific integrated circuit (ASIC) Circuit (IC), a system on chip (SOC), a programmable logic element or a field programmable gate array with a microprocessor (FPGA = Field Programmable Gate Array) may be formed.

The digital storage medium may therefore be machine or computer readable. Thus, some embodiments include a data carrier having electronically readable control signals capable of interacting with a programmable computer system or programmable hardware component such that one of the methods described herein is performed. One embodiment is thus a data carrier (or a digital storage medium or a computer readable medium) on which the program is recorded for performing any of the methods described herein.

In general, embodiments of the present invention may be implemented as a program, firmware, computer program, or computer program product having program code or data, the program code or data operative to perform one of the methods when the program resides on a processor or a computer programmable hardware component expires. The program code or the data can also be stored, for example, on a machine-readable carrier or data carrier. The program code or the data may be present, inter alia, as source code, machine code or bytecode as well as other intermediate code.

Another embodiment is further a data stream, a signal sequence, or a sequence of signals that represents the program for performing any of the methods described herein. The data stream, the signal sequence or the sequence of signals can be configured, for example, to be transferred via a data communication connection, for example via the Internet or another network. Embodiments are also data representative signal sequences suitable for transmission over a network or data communication link, the data representing the program.

For example, a program according to one embodiment may implement one of the methods during its execution by, for example, reading or writing one or more data into memory locations, optionally switching operations or other operations in transistor structures, amplifier structures, or other electrical, optical, magnetic or caused by another operating principle working components. Accordingly, by reading a memory location, data, values, sensor values or other information can be detected, determined or measured by a program. A program can therefore acquire, determine or measure quantities, values, measured variables and other information by reading from one or more storage locations, as well as effect, initiate or execute an action by writing to one or more storage locations and control other devices, machines and components ,

The embodiments described above are merely illustrative of the principles of the present invention. It will be understood that modifications and variations of the arrangements and details described herein will be apparent to others of ordinary skill in the art. Therefore, it is intended that the invention be limited only by the scope of the appended claims and not by the specific details presented in the description and explanation of the embodiments herein.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• CN 202918327 U [0006]
• US 2006115013 A [0006]
• US 8358723 B [0006]
• KR 20070000274A [0007]
• US 2006072679 A [0007]
• FR 2713799 A [0007]

Cited non-patent literature

• IEEE 802.11a [0048]

Claims (15)

Method for identifying a for a selected subcarrier ( 90 ) transmitted symbol ( 92 ) based on one of a plurality of subcarriers ( 90 ; 94a - 94c ) comprehensive received OFDM signal ( 96 ), comprising: determining ( 800 ) at least one receiving parameter characterizing a plurality of subcarriers; for each modulation method of a plurality of possible modulation methods ( 810 ) a usage probability using the reception parameter; and identify ( 820 ) of the modulation method used as the modulation method of the plurality of possible modulation methods, which corresponds to the highest probability of use. The method of claim 1, wherein the receive parameter is a first order statistical parameter comprising a plurality of estimated channel coefficients H D / n ( 160 ), each of the estimated channel coefficients H D / n ( 160 ) a subcarrier n ( 90 ; 94a - 94c ) and an estimated transmission behavior of the subcarrier ( 90 ; 94a - 94c ) corresponding transmission channel over which the symbol of the subcarrier n ( 90 ; 94a - 94c ) of the OFDM signal ( 96 ) Will be received. Method according to claim 2, wherein the reception parameter μ 2 / H to the mean of the squares of the estimated channel coefficients H D / n ( 160 ) of N dynamically modulated subcarriers ( 90 ; 94a - 94c ) corresponds: μ 2 / H = 1 / NΣ N-1 / n = 0 | HD / n | ² . Method according to one of claims 2 or 3, wherein in determining the probability of use a second order statistical parameter of the plurality of channel coefficients is used as a further receiving parameter. The method of claim 4, wherein the further receive parameter σ 2 / H to the mean of a quadratic deviation of the squares of the estimated channel coefficients H D / n ( 160 ) from the reception parameter μ 2 / H corresponds: σ 2 / H = 1 / NΣN-1 / n = 0 (| HD / n | ² - μ 2 / H) ² . Method according to one of claims 2 to 5, wherein in determining the probability of use, a first probability is taken into account, wherein the specific reception parameter for the considered subcarrier n the channel coefficient H D / n ( 160 ) appreciate. Method according to one of claims 2 to 6, wherein in determining the probability of use further a second probability is taken into account, in which certain reception parameter for the considered subcarrier n ( 90 ; 94a - 94c ) to use the modulation method b _{i of} the plurality of I possible modulation methods b ₀ , b ₁ ,..., b _I-1 . Method according to one of claims 2 to 7, wherein in determining the probability of use further a third probability is considered, in which certain channel coefficients H D / n ( 160 ) and assumed modulation method b _i via subcarrier n ( 90 ; 94a - 94c ) the symbol r _n ( 92 ; 150 ) to recieve. The method of claim 8, wherein the third probability is by approximate calculation of the natural logarithm of the log-likelihood function p (r _n | HD / n, b _i) is determined for square and symmetrically arranged constellation points. Method according to one of claims 8 or 9, wherein the use probability p _bi forming the product of the first probability p (| HD / n || μ 2 / H, σ 2 / H, b _i , B) , the second probability p (b _i | μ 2 / H, σ 2 / H, B) and the third probability p (r _n | HD / n, b _i) it is determined: p _bi = p (| HD / n || μ 2 / H, σ 2 / H, b _i , B) · p (b _i | μ 2 / H, σ 2 / H, B) · p (r _n | HD / n, b _i ). The method of claim 10, wherein a plurality of received symbols r _{k, n of} a received signal frame with K OFDM symbols is used to form a common modulation scheme for the K symbols of a signal frame using the common likelihood: p _{bi, k} = p (| HD / n || μ 2 / H, σ 2 / H, b _i , B) · p (b _i | μ 2 / H, σ 2 / H, B) · Π K- 1 / k = 0p (r _{k, n} | HD / n, b _i) to determine. Method according to one of the preceding claims, in which a modulation method for a Time Division Duplex (TDD) OFDM signal is determined. The method of one of claims 2 to 12, further comprising: receiving the plurality of subcarriers ( 90 . 94a -C) comprehensive OFDM signal ( 96 ); and determine the plurality of channel coefficients ( 160 ) for the plurality of subcarriers ( 90 ; 94a - 94c ) by evaluating one for each of the subcarriers ( 90 ; 94a - 94c ) received previously known sequence ( 99 ) with at least one training symbol each. Contraption ( 100 ) for identifying a symbol r _n (for a transmitted over a selected subcarrier) 92 ) based on one of a plurality of subcarriers ( 90 ; 94a - 94c ) comprehensive received OFDM signal ( 96 ), comprising: a classifier ( 110 ), which is formed, at least one of a plurality of subcarriers ( 90 ; 94a - 94c ) characterizing receive parameter; an evaluator ( 120 ) configured to determine, for each modulation method of a plurality of possible modulation methods, a usage probability using the reception parameter; and an identifier ( 130 ) configured to identify the modulation method used as the one modulation method of the plurality of possible modulation methods that corresponds to the highest use probability. A computer program having a program code configured to perform the method of any one of claims 1 to 13 when the computer program runs on a processor.

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