Technical Field

The present invention relates to concepts of transmitting and receiving messages using subband signals.

Background of the invention

In high mobility scenarios, like vehicular communications, robustness in presence of frequency offsets and Doppler frequency is of paramount importance. Standard transmission techniques like Orthogonal Frequency Division Multiplexing (OFDM) are extremely vulnerable to frequency synchronization errors (for example when using narrow subbands).

Carrier synchronization algorithms sync to one carrier offset. They cannot eliminate the effects of Doppler Frequency spread. State of the art techniques to cancel and mitigate frequency synchronous errors in OFDM include polynomial cancellation coding, self-interference cancellation, iterative interference cancellation etc. These techniques necessitate complex receiver structure and are bandwidth inefficient.

In a 5G new radio access network, different use case scenarios are envisaged. In high mobility vehicular scenario or machine type asynchronous communications (MTC), frequency errors are quite significant. Moreover, for 5G non-orthogonal waveform transmission schemes, the receiver structure is quite complex. These schemes also incorporate a self-generated inter carrier interference. A recent OFDM based non-orthogonal waveform is Pulse shaped OFDM (P-OFDM, from Huawei). P-OFDM has self-generated inter carrier interferences.

Due to the aforementioned deficiencies there is a need for an improved concept for transmitting and receiving messages.

Summary of the invention

Embodiments provide a receiver comprising a frequency transformer. The frequency transformer is configured to transform a received signal having a communication bandwidth to output a plurality of first subband signals each having a first bandwidth. Moreover, the frequency transformer is configured to transform the received signal to output a plurality of second subband signals each having a second bandwidth, wherein the first bandwidth and the second bandwidth differ. Furthermore, the receiver is configured to filter the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters. Moreover, the receiver is configured to determine a first message based on one or more of the plurality of first subband signals and to determine a second message based on one or more of the plurality of second subband signals. In general, the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth.

In embodiments a receiver may be implemented using a flexible Fast Fourier Transform (FFT) as frequency transformer, to receive messages transmitted based on pluralities of subband signals (e.g. the plurality of first subband signals and/or the plurality of second subband signals, which may be obtained from transmitters using Inverse Fast Fourier Transforms (IFFTs) with varying sizes), wherein the subband signals may differ in bandwidth.

Moreover, benefits of the receiver are due to the flexible subband bandwidth used for receiving the first message and the second message. For example, when considering receivers moving relative to a transmitter, subcarriers with a broader bandwidth are less prone to Doppler effects and therefore enable easier reception of messages. However, when a receiver is not moving relative to the transmitter, narrower subband bandwidths may be more suitable as higher data rates may then be easier transmittable due to e.g. simpler equalization and more optimal usage of the individual subcarriers. A more optimal usage may for example be that a subcarrier experiencing low fading is transmitting parts of a message with a higher data rate than subcarriers experiencing strong fading. It may also be noted that enabling a more flexible reception of subband bandwidths may enable transmitters with low computational complexity to coexist in a system with transmitters having high computational complexity using narrower subband bandwidths, as fine segmentation may need more computational power due to the higher number of potential subband signals. Furthermore, using pulse shape filters in the receiver (preferably designed according to pulse shape filters used in a transmitter), is beneficial in reducing inter carrier interference. A suitable choice of pulse shape filters can reduce the inter carrier interference such that subband signals of the first subband signals or the second subband signals have negligible influence on neighboring subband signals or an influence which can be removed by interference cancellation techniques. Pulse shaping filters as for example employed for generalized frequency division multiplexing (GFDM), filter bank multicarrier (FBMC) or pulse-shaped OFDM (POFDM/P-OFDM) improve a peak-to-average power ratio (PAPR) when compared to conventional OFDM based systems, which in turn enables usage of simpler and cheaper power amplifiers in a transmitter.

In embodiments the receiver is configured to remove a first signal component from the received signal, wherein the first signal component is based on the first message, to obtain an enhanced received signal. Furthermore, the receiver is configured to provide the plurality of second of subband signals based on the enhanced received signal. The described embodiments uses so called iterative interference cancellation to achieve easier reception of messages. In other words disturbances in the received signal caused by a another message, e.g. the first message, are first removed before receiving and determining the second message. This iterative cancellation may be continued for further iterations, for example the first message may be determined based on a second enhanced signal which may be obtained by removing components due to the second message.

In embodiments the pulse shape filters are of rectangular shape or of bell shape. Using pulse shape filters of rectangular shape results in original OFDM, i.e. the inter carrier interference is zero. However, using bell shape pulse shape filters may introduce inter carrier interference compared to rectangular shape filters but therefore offers a low peak-to-average power ratio (PAPR) which may be beneficial in combination with common analog power amplifiers commonly used in transmitters.

In embodiments the receiver is configured to filter subband signals of the plurality of first subband signals and/or of the plurality of second subband signals with equalization filters. Equalization filters may at least partially compensate the fading effect (i.e. the superposition of multipath propagation or shadowing which may result in attenuation and/or temporal smearing, i.e. dispersion) of a channel between a transmitter and the receiver and therefore simplify reception or determination of messages.

In embodiments the frequency transformer of the receiver is configured to operate on a basis of a first transformation length (a transformation length may be a discrete Fourier transform size, i.e. the number of orthogonal basis functions which may define the subcarriers or subbands), wherein the first transformation length is configured according to a number of the plurality of first subband signals for receiving the first message. Optionally or additionally, the frequency transformer of the receiver is configured to operate on a basis of a second transformation length, wherein the second transformation length is configured according to a number of the plurality of second subband signals for receiving the second message. The described embodiment is beneficial as a single frequency transformer may be used to segment the received signal into the plurality of first and second subband signals, i.e. using a reconfigurable frequency transformer. The frequency transformer may be configured using variable transformation lengths and thereby enable flexible segmentation of the received signal into subband signals. In other words, hardware or electronics can be saved using only a single frequency transformer instead of several frequency transformers using various transformation length.

In embodiments the receiver is configured to select the first transformation length and the second transformation length based on a predefined first transformation length and a predefined second transformation length. Using predefined transformation length avoids for example the necessity of transmitting the transformation length to the receiver thereby reducing transmission overhead.

In embodiments the receiver is configured to obtain the first transformation length and/or the second transformation length from the received signal. The described embodiment is beneficial for use in scenarios where a high flexibility of subband bandwidths may be necessary. The receiver may during operation switch the subband bandwidths based on a transmitted transformation lengths and may therefore offer easy reconfigurability during operation.

In embodiments the receiver comprises a first frequency transformer operating on a basis of the first transformation iength which is configured to obtain the first plurality of subband signals. Moreover, the receiver comprises a second frequency transformer operating on a basis of the second transformation Iength which is configured to obtain the second plurality of subband signals. Having a receiver with multiple frequency transformers enables parallel segmentation of the received signal based on which subband signals are obtained in parallel. Therefore, a time reduction for receiving messages may be achieved compared to using only one frequency transformer. Enabling faster reception may be especially beneficial for real-time applications (i.e. applications requiring a low delay).

Embodiments provide a transmitter for transmitting a message comprising a frequency transformer. The frequency transformer is configured to transform the message into a transmit signal having a communication bandwidth. Moreover, the frequency transformer is configured to selectively segment the transmit signal into a plurality of first subband signals, or into a plurality of second subband signals. Each of the plurality of first subband signals have a first bandwidth and each of the plurality of second subband signals have a second bandwidth different from the first bandwidth. Furthermore, the transmitter is configured to filter the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters

The described transmitter is beneficial in that it flexibly enables the choice of subband bandwidths through selective segmentation. For example, the described transmitter can, preferably when employed in a device which is moving relative to a receiver, choose to segment the communication bandwidth in broad subbands. Resulting in subband signals which are less susceptible to the Doppler effect, caused by the movement. Therefore, a receiver is able to more easily determine a message being transmitted with said broad subbands. Furthermore, the transmitter may choose to use narrow subbands when it is not moving relatively to a receiver and thereby achieve a flat fading for the individual subband signals which can be equalized easily at a receiver. Furthermore, narrow subbands enable a more flexible distribution of data rate among the individual subbands. Pulse shaping filters as employed for GFDM, FBMC or POFDM improve a peak-to-average power ratio (PAPR) when compared to conventional OFDM based systems, which in turn enables usage of simpler and cheaper power amplifiers in the transmitter. Generally, using suitable pulse shape filters in the transmitter (e.g. filters fulfilling the Nyquist inter symbol interference criterion, e.g. root raised cosine), are beneficial in keeping inter carrier interference small and avoid subband-wise inter symbol interference. A suitable choice of pulse shape filters can reduce the inter carrier interference such that subband signals of the first subband signals or the second subband signals have negligible influence on neighboring subband signals. Moreover, analog power amplifiers may benefit from a suitable choice of pulse shape filters due to a resulting small peak-to-average power ratio (PAPR).

An Idea underlying embodiments is that a transmitter may be designed with a flexible subcarrier bandwidth (for example in OFDM or OFDM based non-orthogonal waveform transmission systems (e.g. Generalized Frequency Division Multiplexing (GFDM) or P-

OFDM)). A total system bandwidth (e.g. communication bandwidth) is divided into 'Ν' sub systems, each with a separate number of subcarriers (wherein on subcarriers individual subband signals are transmitted) (preferred numbers of subcarriers may be a power of 2, i.e. 4,8, 16 etc. for efficient use of a FFT as frequency transformer).

In embodiments of various transmitters, IFFTs are used as frequency transformers, wherein each IFFT spans the entire (or total) system (or communication) bandwidth by using a common sampling period (or rate) (among the various transmitters and a receiver). Each transmitter may segment the communication bandwidth with an individual IFFT size/length (transformation length) (N1 , N2, N3, etc) which denotes the number of subcarriers, where a large number generates a narrower subcarrier bandwidth (e.g. subband bandwidth) than a small number.

In embodiments the transmitter is configured to segment the transmit signal into the plurality of first subband signals or into the plurality of second subband signals, based on a predefined transformation length of the frequency transformer. Using predefined transformation length avoids for example the necessity of transmitting the transformation length to the transmitter thereby reducing transmission overhead.

In embodiments the transmitter is configured to segment the transmit signal into the plurality of first subband signals or into the plurality of second subband signals, based on a channel state information. The described embodiment can beneficial use knowledge about the channel to adapt the segmentation accordingly to the state of the channel.

In embodiments the transmitter is configured to use channel state information comprising information about usage of the communication bandwidth. Usage information of the channel can be used to segment the communication bandwidth such that the subbands are obtained which suffer only from little interference due to other users transmitting in the communication bandwidth.

In embodiments the transmitter is configured to use channel state information comprising channel fading information. Using channel fading information is useful to achieve flat fading (i.e. constant fading) with a large (subband) bandwidth such that a segmentation into narrow subbands may not be necessary.

In embodiments the pulse shape filters are of rectangular shape or of bell shape (e.g. root raised cosine). Using pulse shape filters of rectangular shape results in original OFDM, i.e. the inter carrier interference is zero. Using bell shape pulse shape filters may introduce more inter carrier interference compared to rectangular shape filters but therefore may offer a small PAPR which may be beneficial in combination with analog power amplifiers which may be used in the transmitter.

In embodiments of the receiver or the transmitter the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping. Using overlapping frequencies enables efficient use of the common communication bandwidth. However, subband signals out of the subband signals covering frequencies which are not or only partially overlapping are used to transmit or receive messages to limit self-interference.

In embodiments of the receiver or the transmitter the receiver or the transmitter is configured to choose the first bandwidth or the second bandwidth, such that dividing the communication bandwidth by the first bandwidth or by the second bandwidth yields an integer number. Thereby, a fast implementation of a frequency transformer for segmentation of the communication bandwidth may be used. For example, a fast Fourier transform based on powers of 2 may be used as frequency transformer.

Embodiments provide a communication system for transmitting and receiving messages comprising a receiver (according to a receivers described herein), a first transmitter and a second transmitter. The first transmitter is configured to transmit a first message in a transmit signal having a communication bandwidth in a plurality of first subband signals, and the second transmitter is configured to transmit a second message in a transmit signal having the communication bandwidth in a plurality of second subband signals. The first transmitter and the second transmitter may be transmitters as described herein.

The described communication system is beneficial in that enables coexistence of transmitters using different subband bandwidths. Moreover, each transmitter may chose its subband bandwidth (characterizing the subband signals) as is appropriate for its needs or may be advised for example by the receiver to use subband bandwidths appropriate to the receiver. Therefore, the communication system offers a frequency allocation which is more flexible than conventional systems and is especially suitable in mitigating frequency errors like cause by the Doppler effect.

Embodiments provide a method for receiving messages, comprising transforming a received signal having a communication bandwidth to output a plurality of first subband signals, each having a first bandwidth. Moreover, the method comprises transforming the received signal to output a plurality of second subband signals, each having a second bandwidth, wherein the first bandwidth and the second bandwidth differ. Moreover, the method comprises filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters. Further, the method comprises determining a first message based on one or more of the plurality of first subband signals and determining a second message based on one or more of the plurality of second subband signals. The communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth. In embodiments, the method for receiving messages may be supplemented by all features and functionalities described herein with respect to the receiver embodiments.

Embodiments provide a method for transmitting a message, comprising transforming the message into a transmit signal having a communication bandwidth and selectively segmenting the transmit signal into a plurality of first subband signals, or into a plurality of second subband signals. Further, the method comprises filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters. Moreover, each of the plurality of first subband signals have a first bandwidth and each of the plurality of second subband signals have a second bandwidth different from the first bandwidth. In embodiments, the method for transmitting a message may be supplemented by all features and functionalities described herein with respect to the receiver embodiments.

Embodiments provide a method for transmitting and receiving messages, comprising transforming a first message into a transmit signal having a communication bandwidth and segmenting the transmit signal into a plurality of first subband signals. Moreover, the method comprises transforming a second message into the transmit signal and segmenting the transmit signal into a plurality of second subband signals. Moreover, the method comprises filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters. Further, each of the plurality of first subband signals have a first bandwidth and each of the plurality of second subband signals have a second bandwidth different from the first bandwidth and the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth. Furthermore, the

method comprises transforming a received signal having the communication bandwidth to output the plurality of first subband signals, transforming the received signal to output the plurality of second subband signals, filtering the plurality of first subband signals with pulse shape filters and filtering the plurality of second subband signals with pulse shape filters. Moreover, the method comprises determining the first message based on one or more of the plurality of first subband signals and determining the second message based on one or more of the plurality of second of subband signals. Such a method may be supplemented by all features and functionalities described herein with respect to the methods for receiving messages and the methods for transmitting a message.

Brief Description of the Figures

In the following, embodiments of the present invention will be explained with reference to the accompanying drawings, in which:

Fig. 1 shows a block schematic diagram of a receiver according to an embodiment of the invention;

Fig. 2 shows a block schematic diagram of a receiver according

embodiment of the invention;

Fig. 3 shows a schematic diagram of frequency allocation according to embodiments of the invention;

Fig. 4 shows a block schematic diagram of a transmitter according to an embodiment of the invention;

Fig. 5 shows a block schematic diagram of a transmitter according to an embodiment of the invention;

Fig. 6 shows a block schematic diagram of a communication system according to an embodiment of the invention;

Fig. 7 shows a flow chart of a method for receiving messages according to an embodiment of the invention;

Fig. 8 shows a flow chart of a method for transmitting a message according to an embodiment of the invention; and

Fig. 9 shows a flow chart of a method for transmitting and receiving messages according to embodiments of the invention.

Detailed Description of the Embodiments

Fig. 1 shows a receiver 100 according to embodiments of the invention. The receiver comprises a frequency transformer 1 0, pulse shape filters 115 and a message determiner 120.

A received signal 102 having a communication bandwidth is fed to the frequency transformer 110 to obtain a plurality of first subband signals 112 and/or to obtain a plurality of second subband signals 114. Each subband of the plurality of first subband signals 112 comprises a first bandwidth and each subband of the plurality of second subband signals 114 comprises a second bandwidth, wherein the first bandwidth differs from the second bandwidth. The plurality of first subband signals 112a and/or the plurality of second subband signals 114b is provided to the pulse shape filters 115 to revert a filtering commonly performed in a transmitter. Furthermore, the filtered plurality of first subband signals 112b and the filtered plurality of second subband signals 114b are passed to the message determiner 120. The message determiner 120 provides a first message 122 based on the filtered plurality of first subband signals 112b and/or a second message 124 based on the filtered plurality of second subband signals 114b.

Based on the differing subband bandwidths of the pluralities of subband signals the receiver 100 can flexible receive messages from transmitters using varying subband bandwidths. For example, a first transmitter may choose to segment a communication bandwidth of 100MHz into 4 subbands each having 25Mhz and a second transmitter may choose to segment the communication bandwidth into 2 subbands each having 50MHz. The described receiver 100 can flexibly decompose the received signal 102 to obtain the subband signals with varying subband bandwidths transmitted by the transmitters. Further, the receiver 100 may first provide subband signals with 25MHz bandwidth as the plurality of first subband signals and subsequently may provide subband signals with 50MHz bandwidth as the plurality of second subband signals, based on the received signal 102. Alternatively, the receiver 100 may be able to simultaneously retrieve said first and second subband signals based on the received signal 102.

Having the capability to freely choose subband bandwidths enables communication systems (e.g. employing the described receiver 100) which may be more robust for example to the Doppler effect, which is occurring when a receiver and a transmitter are moving relative to each other. Due to the Doppler effect a subcarrier in the case of narrow subbands (which is commonly assumed to be located in the middle of a subband) may be shifted out of the original subband bandwidth and, therefore, may not be retrievable anymore for a receiver with conventional frequency synchronization means. However, using broader subband bandwidths helps to avoid this problem as the frequency of a subcarrier may be less shifted relative to a subband bandwidth. A communication system using for example the receiver 100 can therefore be used to use subband bandwidths when experiencing a strong Doppler spread and revert to narrow subband bandwidths when not. Moreover, using pulse shape filters 115 in the receiver allows for transmitters with an improved PAPR when compared to conventional systems, wherein a small PAPR enables usage of cheap power amplifiers in a transmitter. Furthermore, the receiver 100 may be supplemented by some or all functionalities which are described, in particular, features and functionalities which will be described with respect to receiver 200 in Fig. 2.

Fig. 2 shows a receiver 200 according to embodiments of the invention. The receiver 200 extends the receiver 100 with further optional components. A first processing block 203 comprises digital subcarrier down conversion and CP removal. A further processing block is a serial-to-parallel converter 204. The receiver 200 comprises further a frequency transformer 210, here a FFT with varying block sizes, comparable to the frequency transformer 110. Moreover, the receiver 200 comprises a Non-orthogonal Filtering technique block 215, which may for example perform filtering with pulse shape filters or channel equalization filters. Furthermore, the receiver 200 comprises a demultiplexer 217 which comprises a parallel-to-serial converter. The demultiplexer 217 is controlled through a resource management block 218. Further, the receiver 200 comprises a symbol mapper 220 which is comparable to the message determiner 120. Finally, the receiver 200 comprises also an interference canceller and a decision feedback equalizer both combined in processing block 225.

In digital subcarrier down conversion and CP removal 203 a first received signal 201 is processed. The first received signal 201 may be obtained by first bandpassing an analog antenna signal followed by optional downmixing and analog-to-digital conversion. Digital subcarrier down conversion yields a signal in which the subbands are shifted to a base band and may reduce a sampling rate of the first received signal 201 (optionally including band- or lowpassing). The subband signals may be allocated in appropriate frequency regions in a second received signal 202 for the frequency transformer after processing by the processing block 203. Moreover, a cyclic prefix (CP) may be removed which may be added in the transmitter to combat dispersive effects of the channel (guard interval) and to obtain a linear convolution result from the cyclic convolution obtained from a filtering in the FFT domain. The second received signal 202 is fed to the serial-to-parallel converter 204 to obtain an input block for the Fourier transform performed in the FFT 210. The parallelized received signal 206 is then input to the FFT 210 to obtain a plurality of subband signals 212 (e.g. the first plurality of subband signals 112 or the second plurality of subband signals 114). The plurality of subband signals 212 is subjected to filtering (e.g. with pulse shape filters or equalization filters) in the non-orthogonal filtering technique unit 215 (corresponding to pulse shape filters 115 in receiver 100). The filtering performed in 215 may be aimed at reverting a filtering performed at a transmitter. By choice of appropriate pulse shape filter pairs in a transmitter and the receiver inter carrier interference (i.e. inter subband interference) can be significantly reduced which is introduced by the non-orthogonal filtering (e.g. as performed for GFDM). The filtered plurality of subband signals 216 are input to the demulitplexer 217 which may have obtained knowledge about subband usage through the resource management block 218. Based on the subband usage knowledge the demultiplexer may discard individual subbands knowing that a message was transmitted by a transmitter only on certain subbands. Moreover, the discarded subbands may contain interference, for example from other transmitters, which is best ignored for message determination in the symbol mapper 220. Therefore, the subband signals used to form the serialized subband signal 219 may preferably only contain transmitted components from one transmitter (therefore, unused subband signals may be set to zero in further processing). The symbol demapper 220 then uses the serialized subband signal 219 and demaps this to obtain the bit stream 222, representing the message. For demapping, the demapper 220 may for example use inphase and quadrature demodulation techniques to obtain complex valued signals using for example quadrature amplitude modulation (QAM) or phase shift keying (PSK). The demapper 220 may also employ amplitude shift keying (ASK) wherein information about the message is only obtained from the inphase component (i.e. only real-valued values may be used for determination). Therefrom, the demapper 220 may obtain bits according to a constellation of the employed modulation technique (QAM, PSK, ASK, etc.).

In further iterations the received bitstream 222 (representing for example the first message) is used to remove components thereof in the parallelized received signal 206 and/or in the plurality of subband signals 212. Moreover, in further iterations the FFT 210 may change its block size (transformation length) to enable reception of further transmitters using various FFT block sizes and thereby receive further pluralities of subband signals having potentially varying subband bandwidths. Thereby, messages of further transmitters can be received with higher reception quality as disturbances from other already identified transmitters may have been removed. Compared to receiver 100, receiver 200 preferably performs an iterative reception of the pluralities of subband signals (e.g. the plurality of first subband signals and the plurality of second subband signals). An aspect underlying receiver 200 is a receiver model with adaptive subcarrier bandwidth. Moreover, processing blocks which incorporate more than one functionality (e.g. digital subcarrier downconverter and cyclic prefix remover 203, demultiplexer and serial-to-parallel converter 217, interference canceller and decision feedback equalizer 225 and pulse shape filter and equalizer 215) may be provided in further embodiments as individual processing blocks where only one feature ore functionality may be implemented in.
Claims

1. A receiver (100; 200; 630) comprising:

a frequency transformer (1 10; 210);

wherein the frequency transformer (110; 210) is configured to transform a received signal (102; 201 ; 202; 632) having a communication bandwidth (CB) to output a plurality of first subband signals (112a-b; 212) each having a first bandwidth (SCB1), and

wherein the frequency transformer (1 10; 210) is configured to transform the received signal (102; 201 ; 202; 632) to output a plurality of second subband signals (114a-b; 212) each having a second bandwidth (SCB2),

wherein the first bandwidth (SCB1) and the second bandwidth differ (SCB2), and

wherein the receiver is configured to filter the plurality of first subband signals (112a-b; 212) or the plurality of second of subband signals (114a-b; 212) with pulse shape filters (115; 215),

wherein the receiver (100; 200; 630) is configured to determine a first message (122; 222; 612) based on one or more of the plurality of first subband signals (112a-b; 212),

wherein the receiver is configured to determine a second message (124; 222; 614) based on one or more of the plurality of second subband signals (114a-b; 212),

wherein the communication bandwidth (CB) is larger than the first bandwidth (SCB1) and/or the second bandwidth (SCB2);

wherein the receiver is configured to remove a first signal component from the received signal (201 ; 202; 632), wherein the first signal component is based on the first message (222), to obtain an enhanced received signal, and

wherein the receiver (200; 630) is configured to provide the plurality of second subband signals based on the enhanced received signal.

2. Receiver (200; 630) according to claim 1 , wherein the pulse shape filters (215) are of rectangular shape or of bell shape.

3. Receiver (200; 630) according to claim 1 or claim 2, wherein the receiver (200;

630) is configured to filter subband signals of the plurality of first subband signals and/or of the plurality of second subband signals with equalization filters (215).

4. Receiver (100; 200; 630) according to one of the claims 1 to 3, wherein for receiving the first message the frequency transformer (110; 210) is configured to operate on a basis of a first transformation length, and wherein the first transformation length is configured according to a number of the plurality of first subband signals, and/or

wherein for receiving the second message the frequency transformer (110; 210) is configured to operate on a basis of a second transformation length, and wherein the second transformation length is configured according to a number of the plurality of second subband signals.

5. Receiver (100; 200; 630) according to claim 4, wherein the receiver (100; 200;

630) is configured to select the first transformation length and the second transformation length based on a predefined first transformation length and a predefined second transformation length, or

wherein the receiver (100; 200; 630) is configured to obtain the first transformation length and/or the second transformation length from the received signai (102; 201 , 202; 632).

6. Receiver (100; 200; 630) according to claim 4 or claim 5, wherein the frequency transformer (110; 220) is configured to adjust the transformation length according to a number of subband signals, or

wherein the receiver comprises a first frequency transformer operating on a basis of the first transformation length configured to obtain the first plurality of subband signals, and

wherein the receiver comprises a second frequency transformer operating on a basis of the second transformation length configured to obtain the second plurality of subband signals.

Receiver (100; 200; 630) according to one of the claims 1 to 6, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping.

Receiver (100; 200; 630) according to one of the claims 1 to 7, wherein dividing the communication bandwidth (CB) by the first bandwidth (SCB1) or by the second bandwidth (SCB2) yields an integer number.

A transmitter (400; 500; 610, 620) for transmitting a message comprising a frequency transformer (420; 520) to a receiver according to one of the claims 1 to 8,

wherein the frequency transformer (420; 520) is configured to transform the message into a transmit signal (440; 540; 614; 624) having a communication bandwidth (CB),

wherein the frequency transformer (420; 520) is configured to selectively segment the transmit signal (440; 540; 614; 624) into a plurality of first subband signals, or into a plurality of second subband signals,

wherein the transmitter is configured to filter the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters (415; 515),

wherein each of the plurality of first subband signals have a first bandwidth (SCB1) and wherein each of the plurality of second subband signals have a second bandwidth (SCB2) different from the first bandwidth (SCB1).

10. Transmitter (400; 500; 610, 620) according to claim 9, wherein the transmitter (400; 500; 610, 620) is configured to segment the transmit signal into the plurality of first subband signals or into the plurality of second subband signals, based on a predefined transformation length of the frequency transformer (420; 520).

1 1. Transmitter (400; 500; 610, 620) according to claim 9, wherein the transmitter (400; 500; 610, 620) is configured to segment the transmit signal (440; 540; 614; 624) into the plurality of first subband signals or into the plurality of second subband signals, based on a channel state information.

12. Transmitter (400; 500; 610, 620) according to claim 1 1 , wherein the channel state information comprises information about usage of the communication bandwidth

(CB).

Transmitter (400; 500; 610, 620) according to claim 11 or claim 12, wherein the channel state information comprises channel fading information.

Transmitter according to one of the claims 9 to 13, wherein the pulse shape filters (415; 515) are of rectangular shape or of bell shape.

Transmitter (400; 500; 610, 620) according to one of the claims 9 to 14, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping.

Transmitter (400; 500; 610, 620) according to one of the claims 9 to 15, wherein dividing the communication bandwidth (CB) by the first bandwidth (SCB1) or by the second bandwidth (SCB2) yields an integer number.

Communication system (600) for transmitting and receiving messages (612, 622) comprising

a receiver (630) according to one of the claims 1 to 8, and

a first transmitter (610), transmitting a first message (612) in a transmit signal (614) having a communication bandwidth (CB) in a plurality of first subband signals, and a second transmitter (620), transmitting a second message (622) in a transmit signal (624) having the communication bandwidth (CB) in a plurality of second subband signals.

Communication system (600) according to claim 17, wherein the first transmitter (610) and/or the second transmitter (620) is/are a transmitter (400; 500) according to one of the claims 9 to 16.

Method (700) for receiving messages (122, 124; 222; 612, 622), comprising:

transforming (710) a received signal having a communication bandwidth (CB) to output a plurality of first subband signals each having a first bandwidth (SCB1), and

transforming (720) the received signal to output a plurality of second subband signals each having a second bandwidth (SCB2),

wherein the first bandwidth (SCB1) and the second bandwidth differ (SCB2),

filtering (730) the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters (115; 215), and

determining (740) a first message (122; 612) based on one or more of the plurality of first subband signals (112), and

determining (750) a second message (124; 622) based on one or more of the plurality of second subband signals (114),

wherein the communication bandwidth (CB) is larger than or equal to the first bandwidth (SCB1) and/or the second bandwidth (SCB2),

wherein a first signal component is removed from the received signal (201 ; 202; 632), wherein the first signal component is based on the first message (222), to obtain an enhanced received signal, and

wherein the plurality of second of subband signals are provided based on the enhanced received signal.

20. Method (800) for transmitting a message (401 ; 501 ; 612, 622) to a receiver according to one of the claims 1 to 8, comprising:

selectively segmenting (810) the message into a plurality of first subband signals, or into a plurality of second subband signals,

filtering (820) the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters (115; 215),

transforming (830) the plurality of first subband signals or the plurality of second subband signals (401 ; 501 ; 612, 622) into a transmit signal (440; 540; 614, 624) having a communication bandwidth (CB),

wherein each of the plurality of first subband signals have a first bandwidth (SCB1) and wherein each of the plurality of second subband signals have a second bandwidth (SCB2) different from the first bandwidth (SCB1).

21. Method (900) for transmitting and receiving messages (122, 124; 222; 401 ; 501 ;

612, 622), comprising:

segmenting (910a) a first message into a plurality of first subband signals,

filtering (920a) the plurality of first subband signals with pulse shape filters (115; 215),

transforming (930a) the first plurality of subband signals into a transmit signal having a communication bandwidth (CB),

segmenting (910b) a second message into a plurality of second subband signals,

filtering (920b) the plurality of second subband signals with pulse shape filters (115; 215),

transforming (930b) the second plurality of subband signals into a transmit signal having the communication bandwidth (CB),

wherein each of the plurality of first subband signals have a first bandwidth (SCB1) and wherein each of the plurality of second subband signals have a second bandwidth (SCB2) different from the first bandwidth (SCB1), and wherein the communication bandwidth (CB) is larger than or equal to the first bandwidth (SCB1) and/or the second bandwidth (SCB2)

transforming (940a) a received signal having the communication bandwidth (CB) to output the plurality of first subband signals, and

transforming (940b) the received signal to output the plurality of second subband signals,

filtering (950) the plurality of first subband signals and/or the plurality of second of subband signals with pulse shape filters (115; 215),

determining (960a) the first message based on one or more of the plurality of first subband signals, and

determining (960b) the second message based on one or more of the plurality of second of subband signals,

wherein a first signal component is removed from the received signal (201 ; 202; 632), wherein the first signal component is based on the first message (222), to obtain an enhanced received signal, and

wherein the plurality of second of subband signals are provided based on the enhanced received signal.

Computer program with a program code for performing a method according to one of the claims 19 to 21 , when the computer program runs on a computer or a microcontroller.