RECEIVER, TRANSMITTER, COMMUNICATION SYSTEM FOR SUBBAND COMMUNICATION AND METHODS FOR SUBBAND COMMUNICATION

Abstract

Receiver including a frequency transformer; the frequency transformer being configured to transform a received signal having a communication bandwidth to output a plurality of first subband signals each having a first bandwidth and the frequency transformer being 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 and wherein the receiver is configured to filter the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters; the receiver being configured to determine a first message based on one or more of the plurality of first subband signals and the receiver being configured to determine a second message based on one or more of the plurality of second subband signals; the communication bandwidth being larger than or equal to the first bandwidth and/or the second bandwidth.

Claims

1. A receiver comprising: a frequency transformer; wherein the frequency transformer is configured to transform a received signal comprising a communication bandwidth to output a plurality of first subband signals each comprising a first bandwidth, and wherein the frequency transformer is configured to transform the received signal to output a plurality of second subband signals each comprising a second bandwidth, wherein the first bandwidth and the second bandwidth differ, and wherein the receiver is configured to filter the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters, wherein the receiver is configured to determine a first message based on one or more of the plurality of first subband signals, wherein the receiver is configured to determine a second message based on one or more of the plurality of second subband signals, wherein the communication bandwidth is larger than the first bandwidth and/or the second bandwidth; wherein 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 acquire an enhanced received signal, and wherein the receiver is configured to provide the plurality of second subband signals based on the enhanced received signal.

2. Receiver according to claim 1, wherein the pulse shape filters are of rectangular shape or of bell shape.

3. Receiver according to claim 1, wherein 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.

4. Receiver according to claim 1, wherein for receiving the first message the frequency transformer 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 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 according to claim 4, wherein 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, or wherein the receiver is configured to acquire the first transformation length and/or the second transformation length from the received signal.

6. Receiver according to claim 4, wherein the frequency transformer 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 acquire 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 acquire the second plurality of subband signals.

7. Receiver according to claim 1, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping.

8. Receiver according to claim 1, wherein dividing the communication bandwidth by the first bandwidth or by the second bandwidth yields an integer number.

9. A transmitter for transmitting a message comprising a frequency transformer to a receiver according to claim 1, wherein the frequency transformer is configured to transform the message into a transmit signal comprising a communication bandwidth, wherein 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, 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, wherein each of the plurality of first subband signals comprise a first bandwidth and wherein each of the plurality of second subband signals comprise a second bandwidth different from the first bandwidth.

10. Transmitter according to claim 9, wherein 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.

11. Transmitter according to claim 9, wherein 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.

12. Transmitter according to claim 11, wherein the channel state information comprises information about usage of the communication bandwidth.

13. Transmitter according to claim 11, wherein the channel state information comprises channel fading information.

14. Transmitter according to claim 9, wherein the pulse shape filters are of rectangular shape or of bell shape.

15. Transmitter according to claim 9, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping.

16. Transmitter according to claim 9, wherein dividing the communication bandwidth by the first bandwidth or by the second bandwidth yields an integer number.

17. Communication system for transmitting and receiving messages comprising a receiver according to claim 1, and a first transmitter, transmitting a first message in a transmit signal comprising a communication bandwidth in a plurality of first subband signals, and a second transmitter, transmitting a second message in a transmit signal comprising the communication bandwidth in a plurality of second subband signals.

18. Communication system according to claim 17, wherein the first transmitter and/or the second transmitter is/are a transmitter according to claim 9.

19. Method for receiving messages, comprising: transforming a received signal comprising a communication bandwidth to output a plurality of first subband signals each comprising a first bandwidth, and transforming the received signal to output a plurality of second subband signals each comprising a second bandwidth, wherein the first bandwidth and the second bandwidth differ, filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters, and 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, wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth, wherein a first signal component is removed from the received signal, wherein the first signal component is based on the first message, to acquire an enhanced received signal, and wherein the plurality of second of subband signals are provided based on the enhanced received signal.

20. Method for transmitting a message to a receiver according to claim 1, comprising: selectively segmenting the message into a plurality of first subband signals, or into a plurality of second subband signals, filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters, transforming the plurality of first subband signals or the plurality of second subband signals into a transmit signal comprising a communication bandwidth, wherein each of the plurality of first subband signals comprise a first bandwidth and wherein each of the plurality of second subband signals comprise a second bandwidth different from the first bandwidth.

21. Method for transmitting and receiving messages, comprising: segmenting a first message into a plurality of first subband signals, filtering the plurality of first subband signals with pulse shape filters, transforming the first plurality of subband signals into a transmit signal comprising a communication bandwidth, segmenting a second message into a plurality of second subband signals, filtering the plurality of second subband signals with pulse shape filters, transforming the second plurality of subband signals into a transmit signal comprising the communication bandwidth, wherein each of the plurality of first subband signals comprise a first bandwidth and wherein each of the plurality of second subband signals comprise a second bandwidth different from the first bandwidth, and wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth transforming a received signal comprising the communication bandwidth to output the plurality of first subband signals, and transforming the received signal to output the plurality of second subband signals, filtering the plurality of first subband signals and/or the plurality of second of subband signals with pulse shape filters, 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, wherein a first signal component is removed from the received signal, wherein the first signal component is based on the first message, to acquire an enhanced received signal, and wherein the plurality of second of subband signals are provided based on the enhanced received signal.

22. A non-transitory digital storage medium having a computer program stored thereon to perform the method for receiving messages, the method comprising: transforming a received signal comprising a communication bandwidth to output a plurality of first subband signals each comprising a first bandwidth, and transforming the received signal to output a plurality of second subband signals each comprising a second bandwidth, wherein the first bandwidth and the second bandwidth differ, filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters, and 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, wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth, wherein a first signal component is removed from the received signal, wherein the first signal component is based on the first message, to acquire an enhanced received signal, and wherein the plurality of second of subband signals are provided based on the enhanced received signal, when said computer program is run by a computer.

23. A non-transitory digital storage medium having a computer program stored thereon to perform the method for transmitting a message to a receiver according to claim 1, the method comprising: selectively segmenting the message into a plurality of first subband signals, or into a plurality of second subband signals, filtering the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters, transforming the plurality of first subband signals or the plurality of second subband signals into a transmit signal comprising a communication bandwidth, wherein each of the plurality of first subband signals comprise a first bandwidth and wherein each of the plurality of second subband signals comprise a second bandwidth different from the first bandwidth, when said computer program is run by a computer.

24. A non-transitory digital storage medium having a computer program stored thereon to perform the method for transmitting and receiving messages, the method comprising: segmenting a first message into a plurality of first subband signals, filtering the plurality of first subband signals with pulse shape filters, transforming the first plurality of subband signals into a transmit signal comprising a communication bandwidth, segmenting a second message into a plurality of second subband signals, filtering the plurality of second subband signals with pulse shape filters, transforming the second plurality of subband signals into a transmit signal comprising the communication bandwidth, wherein each of the plurality of first subband signals comprise a first bandwidth and wherein each of the plurality of second subband signals comprise a second bandwidth different from the first bandwidth, and wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth transforming a received signal comprising the communication bandwidth to output the plurality of first subband signals, and transforming the received signal to output the plurality of second subband signals, filtering the plurality of first subband signals and/or the plurality of second of subband signals with pulse shape filters, 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, wherein a first signal component is removed from the received signal, wherein the first signal component is based on the first message, to acquire an enhanced received signal, and wherein the plurality of second of subband signals are provided based on the enhanced received signal, when said computer program is run by a computer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:

[0041] FIG. 1 shows a block schematic diagram of a receiver according to an embodiment of the invention;

[0042] FIG. 2 shows a block schematic diagram of a receiver according to an embodiment of the invention;

[0043] FIG. 3 shows a schematic diagram of frequency allocation according to embodiments of the invention;

[0044] FIG. 4 shows a block schematic diagram of a transmitter according to an embodiment of the invention;

[0045] FIG. 5 shows a block schematic diagram of a transmitter according to an embodiment of the invention;

[0046] FIG. 6 shows a block schematic diagram of a communication system according to an embodiment of the invention;

[0047] FIG. 7 shows a flow chart of a method for receiving messages according to an embodiment of the invention;

[0048] FIG. 8 shows a flow chart of a method for transmitting a message according to an embodiment of the invention; and

[0049] FIG. 9 shows a flow chart of a method for transmitting and receiving messages according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0050] FIG. 1 shows a receiver 100 according to embodiments of the invention. The receiver comprises a frequency transformer 110, pulse shape filters 115 and a message determiner 120.

[0051] 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.

[0052] 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 100 MHz into 4 subbands each having 25 Mhz and a second transmitter may choose to segment the communication bandwidth into 2 subbands each having 50 MHz. 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 25 MHz bandwidth as the plurality of first subband signals and subsequently may provide subband signals with 50 MHz 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.

[0053] 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.

[0054] 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.

[0055] 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 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.).

[0056] 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 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.

[0057] in FIG. 3 a flexible subcarrier bandwidth scheme is shown which illustrates a possible frequency allocation for various transmitters received with for example receivers 100 or 200. Alternatively, the frequency allocation may be used by one transmitter sending multiple messages or a message with different frequency allocations simultaneously. The allocation scheme is presented in FIG. 3 for use in GFDM but may of course also be usable, for example, for OFDM.

[0058] FIG. 3 shows 3 sidebands, sideband 1, sideband 2 and sideband 3, which share the same communication bandwidth and are transmitted using the same frequency range. In sideband 1 a division of the communication bandwidth (CB) into 8 subband signals is illustrated. Each subband signal of sideband 1 therefore has a bandwidth which is one eighth of the CB, illustrated by the subcarrier bandwidth 1 (SCB1). In sideband 2 a division of the CB into 4 subband signals is illustrated. Each subband signal of sideband 2 therefore has a bandwidth which is one fourth of the CB, illustrated by the subcarrier bandwidth 2 (SCB2). In sideband 3 a division of the CB into 2 subband signals is illustrated. Each subband signal of sideband 3 therefore has a bandwidth which is half the CB, illustrated by subcarrier bandwidth 3 (SCB3). A possible communication bandwidth could be 8 MHz which would lead to SCB1=1 MHz, SCB2=2 MHz and SCB3=4 MHz. Moreover, due to the nature of GFDM each sideband has a quadratic block size, i.e. for example a block of sideband 1 can be represented as 88 matrix. In other words, for example for sideband 1, there are eight subband signals (each having a bandwidth of one eighth of the CB) each comprising 8 time samples (spanning an 88 matrix). Therefore, in GFDM a symbol time (length of a block in time samples) is inverse to the subcarrier bandwidth divided by the communication bandwidth (e.g. sideband 1 SCB1/CB=8 symbol time).

[0059] Advantageously, each of the sidebands are only sparsely populated, i.e. messages are only transmitted on selected subcarriers (using only some of the subband signals) of the sidebands. For example, in sideband 1 a transmitter may only use the subbands 301 and 302, which represent the lower fourth of the CB, in sideband 2 a transmitter may transmit a message using only subband 311 which occupies the second fourth of the CB and in sideband 3 a transmitter may use only subband 321 which occupies the upper two fourths of the CB. Thereby, a non-overlapping frequency allocation pattern is chosen which improves reception quality as interference between the subbands is kept small. However, one may also use an overlapping frequency allocation which may still lead to moderate or sufficient reception quality.

[0060] FIG. 4 illustrates a transmitter 400 according to embodiments of the invention. The transmitter 400 comprises a frequency transformer 420 (e.g. a Fourier transformer (advantageously an IFFT)) and pulse shape filters 415. Moreover, the transmitter 400 takes a message 401 as input and transmits, using the frequency transformer 420 and the pulse shape filters 415, a transmit signal 440 to a channel.

[0061] The frequency transformer 420 is configured to transform the message 401 into the transmit signal 440. Therefore, the pulse shape filters 415 segments the message into equally sized subband signals (with equal bandwidth) in the baseband which in turn are transformed to transmit frequencies by the frequency transformer 420. The transmit signal 440 may be obtained by adding up the individual subband signals (obtained by the frequency transformer 420) and further optional upmixing to a desired carrier frequency. Moreover, the transmit signal 440 has a communication bandwidth (analog to the communication bandwidth CB described with respect to the receivers), which can be selectively segmented into the plurality of first subband signals or the plurality of second subband signals. The segmentation is performed by the frequency transformer 420 and the pulse shape filters 415 which may use an optional subband segmentation information to segment the communication bandwidth. Moreover, the optional subband segmentation information may be based on some control information provided externally by some auxiliary device (e.g. a receiver obtaining channel state information (CSI) from another transmitter or a speed indicator for estimating the Doppler drift). Based on the optional subband segmentation information the transmitter may transmit a first message with a plurality of subband signals having a first bandwidth and transmit a second message with a plurality of subband signals having a second bandwidth, wherein the first and the second bandwidth differ.

[0062] Using knowledge for example from channel state information, indicating that non-flat fading channel is observed, i.e. the attenuation is highly varying with frequency, the optional subband segmentation information may indicate to use a finer segmentation yielding narrow bandwidth subband signals exhibiting a flat fading characteristic, i.e. the change of attenuation is only minor within a subband. Moreover, e.g. using speed information the transmitter 400 may perform a coarse segmentation through the pulse shape filters 415 and the frequency transformer 420 when fast movement of the transmitter (relative to a receiver) is indicated (leading to a strong Doppler drift). Coarse segmentation yields broad subbands and therefore increases robustness against Doppler drift by increasing a coherence bandwidth. Moreover, using pulse shape filters 415 helps in obtaining a smaller PAPR than conventional OFDM systems and, therefore, allows the use of simpler (cheaper) power amplifiers in a transmitter (e.g. for radio transmission with a radio frequency RF).

[0063] FIG. 5 shows a block schematic diagram of a transmitter 500 according to embodiments of the invention. The transmitter is similar to the transmitter 400 but is supplemented by further optional features and functionalities by which the transmitter 400 may be extended either entirely or individually.

[0064] The transmitter 500 comprises a symbol mapper 505, a scheduler/multiplexer 510, a pulse shape filter 515 (labelled Non-orthogonal filtering techniques), an IFFT 520, a parallel-to-serial converter 525, a cyclic prefix adder 530 and a digital subcarrier upconverter 535. Furthermore, the transmitter 500 comprises a resource management block 518.

[0065] The transmitter 500 takes as input a message in the shape of a bit stream 501. The bit stream is processed by the symbol mapper 505 to obtain transmit symbols 506. for example QAM, PSK or ASK symbols, representing the message. The transmit symbols 506 are processed in the scheduler/multiplexer 510, allocating transmit symbols 506 to individual subband signals 511, wherein each of the subband signals 511 may at first be baseband signals which are modulated consequently by the IFFT 520 to the individual subband carrier frequency. Before modulation through the IFFT 520 each subband signal 511 is filtered through the pulse shape filter 515. Using pulse shape filters which are bell shaped in the pulse shape filter 515 leads to non-orthogonal OFDM which has the advantage of a lower peak-to-average power ratio (compared to conventional OFDM) which is beneficial for common analog power amplifiers commonly used to transmit signals for example wirelessly. The filtered subband signals 516 are processed in the IFFT which modulates each of the filtered subband signals from the baseband to its subcarrier frequency. Thereby, a plurality of subband signals 521 is obtained. The plurality of subband signals 521 is serialized by the parallel-to-serial converter obtaining the serialized subband signal 526. The cyclic prefix adder 530 adds a cyclic prefix to the serialized subband signal 526. The cyclic prefix is used on one hand to mitigate to dispersive effects of the channel and on the other hand to linearize the result of the cyclic convolution obtained from the IFFT and FFT, as already described with respect to receiver 200. In a further step the baseband transmit signal 531 is upconverted in the digital subcarrier upconverter 535, to shift the center frequency or the carrier frequency of the communication bandwidth to a higher frequency, suitable for transmission, yielding the transmit signal 540. For upconversion, the digital subcarrier upconverter may upsample, bandpass and upmix the baseband transmit signal. Moreover, the individual subband signals obtained from the IFFT may be added up. In further optional steps, the transmit signal 540 may be digital-to-analog converted, bandpassed, upmixed and power amplified to obtain a high frequency transmit signal (e.g. for wireless transmission).

[0066] As described with respect to transmitter 400, the transmitter 500 may transmit the communication bandwidth into subbands with varying bandwidth. This is indicated by the IFFT with varying block sizes 520, which obtains information about the block size for example through the resource management block 518. Furthermore, the pulse shape filter 515 is adjusted to the block size of the IFFT. The block size of the IFFT defines the segmentation, for example a IFFT with a block size of 8 may be used to provide 8 subband signals with equal bandwidth which are comprised in a resulting transmit signal. The switching of the block sizes (segmentation) can be performed for the reasons given with respect to receiver 100, receiver 200 or transmitter 400. Further, the transmitter 500 illustrates variable IFFT sizes coupled to Non-orthogonal Filtering Techniques and processing block having multiple functionalities or features (e.g. the scheduler/multiplexer 510 or the digital subcarrier upconverter) may in embodiments be realized as individual processing blocks (e.g. separate scheduler and multiplexer or digital subcarrier upconverter and a adder for adding IFFT blocks).

[0067] FIG. 6 illustrates a block schematic diagram of a communication system 600, according to embodiments of the invention. The communication system comprises a first transmitter 610, a second transmitter 620 and a receiver 630.

[0068] The first transmitter 610 takes a first message 612 and transforms it into a first transmit signal 614 and transmits it into a channel 640. For transformation the first transmit signal 614 is segmented into a first plurality of subband signals and the first message 612 is distributed among the subband signals. The second transmitter 620 takes a second message 622 and transforms it into a second transmit signal 624 and transmits it into the channel 640. For transformation the second transmit signal 624 is segmented into a second plurality of subband signals and the second message 622 is distributed among the subband signals. The subbands of the first subband signals have a first bandwidth which may differ from the second bandwidth of the subbands of the second subband signals. In the channel 640 the first transmit signal 614 and the second transmit signal 624 add up and are received as the received signal 632 through the channel 640 by the receiver 630. The receiver 630 takes the received signal 632 and provides the first message 612 and the second message 622 as output. Therefore, the receiver 630 segments the transmit signal into the first plurality of subband signals, based upon which the receiver 600 obtains the first message 612, and segments the transmit signal into the second plurality of subband signals, based upon which the receiver 600 obtains the second message 622.

[0069] The receiver 630 may be a transmitter according to transmitters 100 or 200, and the transmitter 610 and 620 may be transmitters according to transmitters 400 or 500. Moreover, the transmitters 610 and 620 may also be conventional transmitters using different subband bandwidths. The latter is advantageous for using legacy hardware (i.e. transmitters in this case) in new transceiver (transmitter+receiver) systems.

[0070] FIG. 7 illustrates a method 700 for receiving messages according to embodiments of the invention. The method 700 comprises transforming 710 a received signal having a communication bandwidth to output a plurality of first subband signals each having a first bandwidth. Further, the method 700 comprises transforming 720 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 700 comprises filtering 730 the plurality of first subband signals or the plurality of second subband signals with pulse shape filters. Further, the method 700 comprises determining 740 a first message based on one or more of the plurality of first subband signals and determining 750 a second message based on one or more of the plurality of second subband signals, wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth. The method steps may be performed in various order for example step 720 may be performed before 710 or 750 before 740. Moreover, the second subband signals may be produced 720 only after determining 730 the first message, wherein the first message may be used to increase reception quality of the second message. The method 700 may be performed by receivers 100, 200 or 630.

[0071] FIG. 8 illustrates a method 800 for transmitting a message according to embodiments of the invention. The method 800 comprises selectively segmenting 810 a message into a plurality of first subband signals, or into a plurality of second subband signals. Further, the method 800 comprises filtering 820 the plurality of first subband signals or the plurality of second subband signals with pulse shape filters. Moreover, the method 800 comprises transforming 830 the plurality of first subband signals or the plurality of second subband signals into a transmit signal having a communication bandwidth. The method 800 may be performed by transmitters 400, 500, 610 or 620.

[0072] FIG. 9 illustrates a method 900 for transmitting and receiving messages 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 and transforming 930a the first plurality of subband signals into a transmit signal having a communication bandwidth. Moreover, the method 900 comprises segmenting 910b a second message into a plurality of second subband signals, filtering 920b the plurality of second subband signals with pulse shape filters and transforming 930b the second plurality of subband signals into a transmit signal having the communication bandwidth, wherein 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 wherein the communication bandwidth is larger than or equal to the first bandwidth and/or the second bandwidth. Furthermore, the method 900 comprises transforming 940 a received signal having the communication bandwidth to output the plurality of first subband signals and transforming 940b the received signal to output the plurality of second subband signals. Further, the method 900 comprises filtering 950 the plurality of first subband signals and/or the plurality of second subband signals with pulse shape filters. Moreover, the method 900 comprises 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. The order in which the method steps are shown here is not restrictive. Further, the method 900 may be performed by a communication system according to the communication system 600.

FURTHER ASPECTS AND CONCLUSIONS

[0073] It has been found that variable subcarrier bandwidth in a Non-orthogonal waveform transmission system provides a flexibility of subcarrier width for more robust transmissions in high mobility vehicular environment in presence of frequency offsets and errors. It has further been found that a Non-orthogonal waveform receiver may mitigate a self-generated inter carrier interference with iterative cancellation. Ideas underlying embodiments improve achievable capacity compared to (conventional) OFDM systems in high velocity scenarios.

[0074] It has further been found that for high mobility vehicular communications, Doppler and other frequency errors are a problem in traditional OFDM/LTE systems. Therefore, an idea underlying embodiments is to have variable subcarrier width along with non-orthogonal waveform transmissions with subcarrier wise pulse shaping technique with reduced out of band leakage. A further idea underlying embodiments is that iterative interference cancellation at the receiver removes self-generated ICIs (inter carrier interferences) and improves system performance compared to existing technologies.

[0075] Embodiments relate to incorporating an adaptive and flexible subcarrier bandwidth for OFDM based non orthogonal waveform and/or a variable/flexible subcarrier bandwidth for non-orthogonal waveform in robust vehicular communication. Moreover, embodiments relate to wireless communication, digital or optical communications involving modulated signals/waveforms. Furthermore, embodiments relate to adaptive subcarrier width for non-orthogonal transmissions with iterative Interference cancellation in vehicular scenarios. An idea underlying embodiments is mitigating Doppler and other frequency errors in high velocity communications with adaptive subcarrier width and non-orthogonal transmission technique.

[0076] In embodiments an OFDM based non-orthogonal waveform transmission system, a P-OFDM transmitter is designed with flexible subcarrier bandwidth. A total system bandwidth (communication bandwidth) is divided into N sub systems, each with a separate number of subcarriers (power of 2, 4, 8, 16 etc.). A loss of orthogonality due to this, is added onto the non-orthogonality present due to pulse shaping of subcarriers in P-OFDM transmitter.

[0077] In embodiments each inverse fast fourier transform (IFFT) spans the entire system bandwidth by using the same sampling period. In each IFFT, (N1, N2, N3, etc) denotes the number of sub carriers, where larger numbers generate narrower sub carriers bandwidths. It can be noted that only a fraction of the subcarriers in each IFFT may be activated (the number of active sub carriers in each IFFT can be made to vary), and that the active sub carriers of the different groups may be selected such that the frequency band spanned by the different groups do not overlap. A user is allocated to a particular sub carrier group, whose sub carrier bandwidth suits the requirement of the user's conditions optimally. In embodiments a receiver (e.g., a mobile device a non-base station device) having a flexible FFT can be implemented as a user will need only one type of sub carrier at a time, while at the base station as many IFFTs as there are sub carrier types may be used. The time frequency diagram of the signal can be represented as in FIG. 3.

[0078] In embodiments an interference mitigation performed at the receiver may cancel the self-interference due to the non-orthogonal subcarriers and also the interference due to the effect of variable subcarrier width. In embodiments advanced receivers (i.e. receiver methods) like MMSE (minimum mean squared error) or decision feedback receivers may be able to reduce the interference between the subcarriers and the bands. For better performance, in embodiments turbo equalizers may be used to mitigate the ICI (inter carrier interference) and ISI (inter symbol interference). In embodiments an iterative interference canceler at the receiver may give theoretical BER (bit error rate) performance. In presence of frequency errors and Doppler spread, the capacity of this scheme, employed in embodiments, my bet better than that of OFDM or P-OFDM.

[0079] Furthermore, embodiments yield a reduced peak-to-average power ratio (PAPR) and are more robust to frequency errors. Moreover, in embodiments iterative interference cancellation techniques at the Rx (receiver) for Non-orthogonal waveforms removes (or reduces) the self-interference created by variable subcarrier bandwidths. Furthermore, embodiments according to the invention in high mobility vehicular scenarios or asynchronous MTC (machine type communication) scenarios, using differential subcarrier P-OFDM or OFDM based non orthogonal waveforms lead to higher (channel) capacity than that of standard OFDM suffering from frequency offsets in the mentioned scenarios.

[0080] According to aspects of the invention the pulse shape filters may be combined with the frequency transformer using a polyphase network, i.e. a discrete fourier transform filterbank (see P. P. Vaidyanathan, Multirate systems and filter banks, Prentice Hall, Englewood Cliffs, 1993). Moreover, the pulse shape filters may be applied after upsampling of the message in a transmitter such that the upsampled message is a weighted unit impulse train with zeros in between the unit impulses, wherein the number of zeros corresponds to a upsampling rate. Furthermore, in embodiments of receivers and transmitters the order in which pulse shape filters and frequency transformer are arranged can be changed (e.g. by using a filter bank for the pulse shape filters, e.g. using modulated prototype filters).

[0081] Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, one or more of the most important method steps may be executed by such an apparatus.

[0082] Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

[0083] Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

[0084] Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.

[0085] Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

[0086] In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

[0087] A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, the digital storage medium or the recorded medium are typically tangible and/or non-transitionary.

[0088] A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet.

[0089] A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

[0090] A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

[0091] A further embodiment according to the invention comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver.

[0092] In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are performed by any hardware apparatus.

[0093] The apparatus described herein may be implemented using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0094] The apparatus described herein, or any components of the apparatus described herein, may be implemented at least partially in hardware and/or in software.

[0095] The methods described herein may be performed using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0096] The methods described herein, or any components of the apparatus described herein, may be performed at least partially by hardware and/or by software.

[0097] Yet further embodiments are now described. [0098] A 1.sup.st embodiment provides a receiver (100; 200; 630) comprising: [0099] a frequency transformer (110; 210); [0100] wherein the frequency transformer (110; 210) is configured to transform a received signal having a communication bandwidth (CB) to output a plurality of first subband signals (112a-b; 212) each having a first bandwidth (SCB1), and [0101] wherein the frequency transformer (110; 210) is configured to transform the received signal to output a plurality of second subband signals (114a-b; 212) each having a second bandwidth (SCB2), [0102] wherein the first bandwidth (SCB1) and the second bandwidth differ (SCB2), and [0103] 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), [0104] 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), [0105] 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), and [0106] wherein the communication bandwidth (CB) is larger than or equal to the first bandwidth (SCB1) and/or the second bandwidth (SCB2). [0107] A 2.sup.nd embodiment provides the receiver (200; 630) according to the 1.sup.st embodiment, 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 [0108] wherein the receiver (200; 630) is configured to provide the plurality of second of subband signals based on the enhanced received signal. [0109] A 3.sup.rd embodiment provides the receiver (200; 630) according to the 1.sup.st embodiment or according to the 2.sup.nd embodiment, wherein the pulse shape filters (215) are of rectangular shape or of bell shape. [0110] A 4.sup.th embodiment provides the receiver (200; 630) according to any one of the 1.sup.st to 3.sup.rd embodiments, 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). [0111] A 5.sup.th embodiment provides the receiver (100; 200; 630) according to any one of the 1st to 4.sup.th embodiments, 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 [0112] 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. [0113] A 6.sup.th embodiment provides the receiver (100; 200; 630) according to the 5.sup.th embodiment, 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 [0114] wherein the receiver (100; 200; 630) is configured to obtain the first transformation length and/or the second transformation length from the received signal (102; 201, 202; 632). [0115] A 7.sup.th embodiment provides the receiver (100; 200; 630) according to the 5.sup.th embodiment or according to the 6.sup.th embodiment, wherein the frequency transformer (110; 220) is configured to adjust the transformation length according to a number of subband signals, or [0116] 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 [0117] 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. [0118] An 8.sup.th embodiment provides the receiver (100; 200; 630) according to any one of the 1.sup.st to 7.sup.th embodiments, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping. [0119] A 9.sup.th embodiment provides the receiver (100; 200; 630) according to any one of the 1.sup.st to 8.sup.th embodiments, wherein dividing the communication bandwidth (CB) by the first bandwidth (SCB1) or by the second bandwidth (SCB2) yields an integer number. [0120] 10th embodiment provides a transmitter (400; 500; 610, 620) for transmitting a message comprising a frequency transformer (420; 520), [0121] 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), [0122] 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, [0123] 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), [0124] 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). [0125] An 11.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to the 10.sup.th embodiment, 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). [0126] A 12.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to the 10.sup.th embodiment, 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. [0127] A 13.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to the 12.sup.th embodiment, wherein the channel state information comprises information about usage of the communication bandwidth (CB). [0128] A 14.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to the 12.sup.th embodiment or according to the 13.sup.th embodiment, wherein the channel state information comprises channel fading information. [0129] A 15.sup.th embodiment provides the transmitter according to any one of the 10.sup.th to 14.sup.th embodiments, wherein the pulse shape filters (415; 515) are of rectangular shape or of bell shape. [0130] A 16.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to any one of the 10.sup.th to 15.sup.th embodiments, wherein the plurality of first subband signals and the plurality of second subband signals each cover frequencies which are overlapping. [0131] A 17.sup.th embodiment provides the transmitter (400; 500; 610, 620) according to any one of the 10.sup.th to 16.sup.th embodiments, wherein dividing the communication bandwidth (CB) by the first bandwidth (SCB1) or by the second bandwidth (SCB2) yields an integer number.

[0132] An 18.sup.th embodiment provides a communication system (600) for transmitting and receiving messages (612, 622) comprising [0133] a receiver (630) according to any one of the 1.sup.st to 9.sup.th embodiments, and [0134] 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 [0135] 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. [0136] A 19.sup.th embodiment provides the communication system (600) according to the 18.sup.th embodiment, wherein the first transmitter (610) and/or the second transmitter (620) is/are a transmitter (400; 500) according to one of the claims 10 to 17. [0137] A 20.sup.th embodiment provides a method (700) for receiving messages (122, 124; 222; 612, 622), comprising: [0138] 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 [0139] transforming (720) the received signal to output a plurality of second subband signals each having a second bandwidth (SCB2), [0140] wherein the first bandwidth (SCB1) and the second bandwidth differ (SCB2), [0141] filtering (730) the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters (115; 215), and [0142] determining (740) a first message (122; 612) based on one or more of the plurality of first subband signals (112), and [0143] determining (750) a second message (124; 622) based on one or more of the plurality of second subband signals (114), [0144] wherein the communication bandwidth (CB) is larger than or equal to the first bandwidth (SCB1) and/or the second bandwidth (SCB2). [0145] A 21.sup.st embodiment provides a method (800) for transmitting a message (401; 501; 612, 622), comprising: [0146] selectively segmenting (810) the message into a plurality of first subband signals, or into a plurality of second subband signals, [0147] filtering (820) the plurality of first subband signals or the plurality of second of subband signals with pulse shape filters (115; 215), [0148] 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), [0149] 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). [0150] A 22.sup.nd embodiment provides a method (900) for transmitting and receiving messages (122, 124; 222; 401; 501; 612, 622), comprising: [0151] segmenting (910a) a first message into a plurality of first subband signals, [0152] filtering (920a) the plurality of first subband signals with pulse shape filters (115; 215), [0153] transforming (930a) the first plurality of subband signals into a transmit signal having a communication bandwidth (CB), [0154] segmenting (910b) a second message into a plurality of second subband signals, [0155] filtering (920b) the plurality of second subband signals with pulse shape filters (115; 215), [0156] transforming (930b) the second plurality of subband signals into a transmit signal having the communication bandwidth (CB), [0157] 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) [0158] transforming (940a) a received signal having the communication bandwidth (CB) to output the plurality of first subband signals, and [0159] transforming (940b) the received signal to output the plurality of second subband signals, [0160] filtering (950) the plurality of first subband signals and/or the plurality of second of subband signals with pulse shape filters (115; 215), [0161] determining (960a) the first message based on one or more of the plurality of first subband signals, and [0162] determining (960b) the second message based on one or more of the plurality of second of subband signals. [0163] A 23.sup.rd embodiment provides a computer program with a program code for performing a method according to any one of the 20.sup.th to 22.sup.nd embodiments, when the computer program runs on a computer or a microcontroller.

[0164] While this invention has been described in terms of several advantageous embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.