Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2626—Arrangements specific to the transmitter only
  • H04L27/2627—Modulators
  • H04L27/2634—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
  • H04B7/0478—Special codebook structures directed to feedback optimisation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
  • H04B7/0636—Feedback format
  • H04B7/0639—Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
  • H04B7/0658—Feedback reduction
  • H04B7/066—Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2626—Arrangements specific to the transmitter only
  • H04L27/2627—Modulators
  • H04L27/264—Pulse-shaped multi-carrier, i.e. not using rectangular window
  • H04L27/26416—Filtering per subcarrier, e.g. filterbank multicarrier [FBMC]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2647—Arrangements specific to the receiver only
  • H04L27/2649—Demodulators
  • H04L27/26534—Pulse-shaped multi-carrier, i.e. not using rectangular window
  • H04L27/2654—Filtering per subcarrier, e.g. filterbank multicarrier [FBMC]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2647—Arrangements specific to the receiver only
  • H04L27/2649—Demodulators
  • H04L27/26524—Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation

Definitions

• the present invention relates to the field of wireless communications. More specifically, the present invention relates to a transmitter for transmitting a plurality of multicarrier modulation signals over a communication channel, a receiver for receiving a plurality of multicarrier modulation signals over a communication channel as well as corresponding methods.
• Multicarrier modulation (MCM) schemes such as OFDM (orthogonal frequency-division multiplexing), have become one of the major transmission techniques in modern communication systems.
• MCM Multicarrier modulation
• OFDM orthogonal frequency-division multiplexing
• MIMO multiple input multiple output
• precoding techniques have been widely adopted in order to achieve a higher spectral efficiency.
• the channel state information (CSI) is measured and quantized at the receiver side and fed back into the reverse channel. Due to the capacity limit of the feedback channel, it is often the case that only a downsampled (e.g. in frequency domain) precoder matrix indicator (PMI) is fed back to the transmitter. Based on the block selective PMI, the precoder matrix is interpolated based on the subcarrier granularity using certain upsampling filters. At the receiver side, a corresponding equalization is applied to compensate the effective channels including the precoding effect. In TDD systems reverse-link estimation can be used.
• PMI precoder matrix indicator
• the precoding matrix is identical for subcarriers belonging to the same precoding subband.
• This procedure implies the usage of a rectangular shaping window for upsampling to apply the PMI on the subcarrier level.
• the one-tap equalizer is applied at the receiver, which means one equalizer factor is used to compensate the distortion on one subcarrier.
• the direct application of block-wise precoding and equalization procedure is feasible, but may introduce some challenges.
• a second known solution is based on an interpolation-based precoding and partial feedback for MIMO-OFDM systems.
• the receiver sends information about a fraction of the CSI/beamforming vectors to the transmitter. Then, the transmitter reconstructs the beamforming vectors for all the subcarriers.
• This scheme can be considered as the special case of block-wise processing where the block granularity is one subcarrier.
• block-wise processing fails to compensate for a severely selective channel fading.
• the conventional block-wise processing requires the channel response to remain quasi-static within one block.
• the per-subcarrier equalization system assumes a flat fading on subcarrier-level. If the maximum channel delay exceeds the cyclic prefix (CP) length of the OFDM system, this quasi-static assumption in the frequency domain does not hold any more and the system encounters severe
• CP cyclic prefix
• FBMC/OQAM attains the real-valued orthogonality by relying on the similarity of the channels on these two subcarriers. In other words, assuming the channel is locally "flat" within the two adjacent subcarriers, this orthogonality is preserved.
• the conventional block-wise precoding scheme such as the one adopted by the LTE standard cited above, it effectively results in a non-flat (discontinuous) channel between the subcarriers at the block boundaries.
• the orthogonality between the two edge subcarriers can barely be maintained and therefore leads to substantial inter-block interference.
• MIMO processing techniques are widely applied in the currently known communication systems due to the potential spectral efficiency gain, diversity gain, etc.
• MCM systems e.g., OFDM, FMT (Filtered Multitone modulation), FBMC/OQAM
• OFDM Orthogonal Component Interference
• FMT Field-Multitone modulation
• FBMC/OQAM Binary Multitone modulation
• the invention relates to a transmitter for transmitting a plurality of MCM (multicarrier modulation) signals over a communication channel to a receiver, wherein each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain.
• the transmitter comprises a sampler configured to sample each MCM signal at a plurality of sampling points in the frequency domain, wherein two subsequent, i.e.
• neighboring sampling points of the plurality of sampling points define a sampling point frequency spacing in the frequency domain and wherein the ratio between the intercarrier frequency spacing and the sampling point frequency spacing is defined by an oversampling factor K, wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2, a precoder configured to precode the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain, i.e. at each sampling point of the plurality of sampling points in the frequency domain, on the basis of a precoding matrix defined per sampling point of the plurality of sampling points in the frequency domain, and a plurality of transmit antennas configured to transmit the plurality of precoded MCM signals over the communication channel to the receiver.
• an oversampling factor K wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2
• a precoder configured to precode the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain, i.e
• an improved transmitter allowing, in particular, to compensate the performance degradation of MCM systems in severe frequency-selective scenarios and to alleviate inter-block interference of the block-wise transmission for the case of relaxed orthogonality.
• the sampler comprises an upsampler and a filter bank configured to sample each MCM signal at the plurality of sampling points in the frequency domain.
• the filter bank is a fast-convolution filter bank comprising an IFFT unit and an overlap-add unit or overlap-save unit and the precoder is arranged downstream of the IFFT unit and upstream of the overlap-add unit or the overlap-save unit.
• the precoder is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of channel state information associated with the communication channel.
• the precoder is configured to obtain the channel state information associated with the communication channel on the basis of a pilot signal received from the receiver and/or the precoder is configured to obtain the channel state information associated with the communication channel from the receiver in response to a pilot signal transmitted to the receiver.
• the channel state information is defined for the plurality of subcarriers, i.e. for the plurality of subcarrier frequencies
• the precoder is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain by interpolating the channel state information associated with the communication channel at the plurality of sampling points in the frequency domain, for which no channel state information is available, i.e. defined, and by determining the precoding matrix per sampling point of the plurality of sampling points in the frequency domain on the basis of the channel state information at the plurality of sampling points in the frequency domain.
• the precoder is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain by interpolating the channel state information associated with the communication channel at the plurality of sampling points in the frequency domain, for which no channel state information is available, on the basis of interpolation parameters provided by the receiver, in particular the oversampling factor K.
• the precoder is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of a precoder matrix indicator provided by the receiver and wherein the precoder is configured to determine the precoding matrix at the plurality of sampling points in the frequency domain by selecting a precoding matrix from a predefined set, i.e. codebook, of precoding matrices on the basis of the precoder matrix indicator, wherein each precoding matrix of the predefined set of precoding matrices is defined at the plurality of subcarriers, i.e. at the plurality of subcarrier frequencies, and by interpolating the selected precoding matrix at the plurality of sampling points in the frequency domain, for which the precoding matrix is not defined, i.e. not available.
• the invention relates to a receiver for receiving a plurality of MCM, i.e. multicarrier modulation signals over a communication channel from a transmitter, wherein each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain, wherein the receiver comprises: a plurality of receive antennas configured to receive the plurality of MCM signals over the communication channel; and an equalizer configured to equalize the plurality of MCM signals per sampling point of a plurality of sampling points in the frequency domain, i.e.
• each sampling point of the plurality of sampling points in the frequency domain on the basis of an equalization matrix defined per sampling point of the plurality of sampling points in the frequency domain, wherein two subsequent, i.e. neighboring sampling points of the plurality of sampling points define a sampling point frequency spacing in the frequency domain and wherein the ratio between the intercarrier frequency spacing and the sampling point frequency is defined by an oversampling factor K, wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• an improved receiver allowing, in particular, to compensate the performance degradation of MCM systems in severe frequency-selective scenarios and to alleviate inter-block interference of the block-wise transmission for the case of relaxed orthogonality.
• the receiver is configured to provide channel state information associated with the communication channel to the transmitter on the basis of at least one pilot signal from the transmitter, wherein the channel state information allows the transmitter to determine a precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain.
• the receiver according to the first is configured to provide channel state information associated with the communication channel to the transmitter on the basis of at least one pilot signal from the transmitter, wherein the channel state information allows the transmitter to determine a precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain.
• the receiver is further configured to provide interpolation parameters to the transmitter for interpolating the channel state information associated with the communication channel at the plurality of sampling points in the frequency domain.
• the receiver is configured to determine a precoder matrix indicator on the basis of at least one pilot signal from the transmitter and to provide the precoder matrix indicator to the transmitter allowing the transmitter to determine the precoding matrix per sampling point of the plurality of sampling points in the frequency domain by selecting a precoding matrix from a predefined set, i.e. codebook, of precoding matrices on the basis of the precoder matrix indicator, wherein each precoding matrix of the predefined set of precoding matrices is defined at the plurality of subcarriers, i.e. at the plurality of subcarrier frequencies, and by interpolating the selected precoding matrix at the plurality of sampling points in the frequency domain, for which the precoding matrix is not defined.
• the invention relates to a method for transmitting a plurality of MCM, i.e. multicarrier modulation signals over a communication channel to a receiver, wherein each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain, wherein the method comprises: sampling each MCM signal at a plurality of sampling points in the frequency domain, wherein two subsequent, i.e. neighboring sampling points of the plurality of sampling points define a sampling point frequency spacing in the frequency domain and wherein the ratio between the intercarrier frequency spacing and the sampling point frequency spacing is defined by an
• oversampling factor K precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of a precoding matrix defined per sampling point of the plurality of sampling points in the frequency domain, and transmitting the plurality of precoded MCM signals over the communication channel to the receiver.
• the method according to the third aspect of the invention can be performed by the transmitter according to the first aspect of the invention. Further features of the method according to the third aspect of the invention result directly from the functionality of the transmitter according to the first aspect of the invention and its different implementation forms.
• the invention relates to a method for receiving a plurality of MCM, i.e. multicarrier modulation, signals over a communication channel from a transmitter, wherein each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring, subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain, wherein the method comprises: receiving the plurality of MCM signals over the communication channel; and equalizing the plurality of MCM signals per sampling point of a plurality of sampling points in the frequency domain on the basis of an equalization matrix defined per sampling point of the plurality of sampling points in the frequency domain, wherein two subsequent, i.e.
• sampling point frequency spacing in the frequency domain and wherein the ratio between the sampling point frequency spacing and the intercarrier frequency spacing is defined by an oversampling factor K, wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• the method according to the fourth aspect of the invention can be performed by the receiver according to the second aspect of the invention. Further features of the method according to the fourth aspect of the invention result directly from the functionality of the receiver according to the second aspect of the invention and its different implementation forms.
• the invention relates to a computer program comprising program code for performing the method according to the third aspect or the fourth aspect of the invention when executed on a computer.
• the invention can be implemented in hardware and/or software.
• FIG. 1 shows a schematic diagram of a transmitter according to an embodiment in communication with a receiver according to an embodiment.
• Fig. 2 shows a schematic diagram illustrating the steps of a method for transmitting a plurality of MCM signals according to an embodiment.
• Fig. 3 shows a schematic diagram illustrating the steps of a method for receiving a plurality of MCM signals according to an embodiment.
• Fig. 4 shows a schematic diagram of a transmitter according to an embodiment in communication with a receiver according to an embodiment.
• Fig. 5 shows the BLER performance of embodiments of the invention in comparison with the prior art for the case of a synchronous transmission
• Fig. 6 shows the BLER performance of embodiments of the invention in comparison with the prior art for the case of a synchronous transmission.
• corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures.
• embodiments with different functional blocks or processing units are described, which are connected with each other or exchange signals. It will be appreciated that the present invention covers embodiments as well, which include additional functional blocks or processing units that are arranged between the functional blocks or processing units of the embodiments described below.
• FIG. 1 shows a schematic diagram of a wireless communication system comprising a transmitter 101 according to an embodiment and a receiver 121 according to an embodiment configured to communicate via a communication channel 150.
• the transmitter 101 is configured to transmit a plurality of MCM (multicarrier modulation) signals over the communication channel 150 to the receiver 121 , wherein each MCM signal comprises a plurality of subcarriers and wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain.
• MCM multicarrier modulation
• the transmitter 101 comprises a sampler 103 configured to sample each MCM signal at a plurality of sampling points in the frequency domain, wherein two subsequent, i.e.
• the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• the intercarrier frequency spacing can be 15 kHz and the sampling point frequency spacing can be 3.75 kHz for an oversampling factor K equal to 4.
• the transmitter 101 comprises a precoder 105 configured to precode the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of a precoding matrix defined per sampling point of the plurality of sampling points in the frequency domain.
• the precoder 105 is configured to precode the plurality of MCM signals at each sampling point of the plurality of sampling points in the frequency domain on the basis of a precoding matrix defined at each sampling point of the plurality of sampling points.
• the transmitter 101 comprises a plurality of transmit antennas 107 configured to transmit the plurality of precoded MCM signals over the communication channel 150 to the receiver 121 .
• the receiver 121 is configured to receive a plurality of MCM signals over the communication channel 150 from the transmitter 101 .
• the receiver 121 comprises a plurality of receive antennas 127 configured to receive the plurality of MCM signals over the communication channel 150.
• Each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain.
• the receiver 121 comprises an equalizer 125 configured to equalize the plurality of MCM signals per sampling point of a plurality of sampling points in the frequency domain, i.e.
• oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• M u (M u ⁇ N) subcarriers among N subcarriers are assigned to a user u being equipped with the receiver 121 , the sub-frequency-tone index in the oversampling domain can be denoted by I e ⁇ 1,2, ... , KM U + K - 1 ⁇ , where K is the oversampling factor.
• a precoding matrix V m can be applied using the precoder 105 at the transmitter 101 .
• the following signal model holds:
• the equalization can be performed by the equalizer 125 in the oversampling domain based on the effective CSI including the effect of precoding.
• the input signal of the equalizer 125 in the frequency domain can be expressed as:
• n m l e C NR X1 is the additive white Gaussian noise vector on the Z-th tone and the m- th symbol.
• the equalization is performed by the equalizer 125 also in the oversampling domain.
• FIG. 2 shows the steps of a method 200 according to an embodiment for transmitting a plurality of MCM signals over the communication channel 150 to the receiver 121 .
• Each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e. neighboring subcarriers of the plurality of subcarriers define an intercarrier frequency spacing in the frequency domain.
• the method 200 comprises a first step 201 of sampling each MCM signal at a plurality of sampling points in the frequency domain, wherein two subsequent, i.e. neighboring sampling points of the plurality of sampling points define a sampling point frequency spacing in the frequency domain and wherein the ratio between the intercarrier frequency spacing and the sampling point frequency spacing is defined by an oversampling factor K, wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• the method 200 comprises a further step 203 of precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of a precoding matrix defined per sampling point of the plurality of sampling points in the frequency domain.
• the method 200 comprises a further step 205 of transmitting the plurality of precoded MCM signals over the communication channel 150 to the receiver 121 .
• FIG. 3 shows the steps of a method 300 according to an embodiment for receiving a plurality of MCM signals over the communication channel 150 from the transmitter 101 .
• Each MCM signal comprises a plurality of subcarriers, wherein two subsequent, i.e.
• the method 300 comprises a first step 301 of receiving the plurality of MCM signals over the communication channel 150.
• the method 300 comprises a further step 303 of equalizing the plurality of MCM signals per sampling point of a plurality of sampling points in the frequency domain on the basis of an equalization matrix defined per sampling point of the plurality of sampling points in the frequency domain, wherein two subsequent, i.e. neighboring sampling points of the plurality of sampling points define a sampling point frequency spacing in the frequency domain and wherein the ratio between the sampling point frequency spacing and the intercarrier frequency spacing is defined by an oversampling factor K, wherein the oversampling factor K is greater than 1 , in particular an integer equal to or greater than 2.
• the transmitter 101 comprises in addition to the sampler 103, the precoder 105 and the plurality of transmit antennas 107 (for the sake of clarity not shown in figure 4) a symbol mapping unit 109, a resource mapping unit 1 1 1 , an IFFT unit 1 13, an parallel-to-serial conversion unit 1 15, an interpolation unit 1 17 and a codebook 1 19.
• a symbol mapping unit 109 for the sake of clarity not shown in figure 4
• a resource mapping unit 1 1 1 1 for the sake of clarity not shown in figure 4
• an IFFT unit 1 13 for the sake of clarity not shown in figure 4
• an interpolation unit 1 17 for the sake of clarity not shown in figure 4
• the receiver 121 comprises in addition to the plurality of receive antennas 127 (for the sake of clarity not shown in figure 4) and the equalizer 125 a serial-to-parallel conversion unit 135, a FFT unit 133, a resource demapping unit 131 , a filter bank 123b, a downsampler 123a and a symbol demapping unit 129. Moreover, the receiver 121 can comprise a channel (state information) estimation unit 137 and a downsampling unit 139. These components of the embodiment of the transmitter 121 shown in figure 4 will be described in more detail further below.
• the sampler 103 of the transmitter 101 comprises an upsampler 103a and a filter bank 103b configured to sample each MCM signal at the plurality of sampling points in the frequency domain.
• the filter bank 103b can be implemented as fast-convolution filter bank, which could also include the IFFT unit 1 13 shown in figure 4 as well as an overlap-add unit or an overlap-save unit (not shown in figure 4).
• the precoder 105 would be arranged downstream of the IFFT unit 1 13 and upstream of the overlap-add unit or the overlap-save unit and, thus, could take advantage of the processing in the oversampling domain already implemented in a conventional fast-convolution filter bank.
• the symbol mapping unit 109 of the transmitter 101 shown in figure 4 is implemented for channel coding and modulation by mapping from bit-to-symbol.
• the resource mapping unit 1 1 1 of the transmitter 101 shown in figure 4 is implemented for mapping payload symbols together with reference symbols to a time-frequency resource grid for each transmission block.
• the (synthesis) filter bank 103b of the transmitter 101 shown in figure 4 is implemented for modulating and filtering the MCM signals in the frequency domain.
• the synthesis filter bank 103b can be based on a frequency spreading structure.
• the IFFT or IDFT unit 1 13 and the parallel-to-serial conversion unit 1 15 of the transmitter 101 shown in figure 4 are implemented for transferring the MCM signal from each antenna to the time domain and transforming from parallel to serial bit streams.
• the IFFT or IDFT unit 1 13 will be configured to operate on the basis of a size KN, where K is the oversampling factor and N is the number of subcarriers.
• the FFT or DFT unit 133 and the serial-to-parallel conversion unit 135 of the receiver 121 shown in figure 4 are implemented to transfer each signal from each antenna to the frequency domain and to transform from serial to parallel bit streams. As in the case of the IFFT or IDFT unit 1 13 of the transmitter, the FFT or DFT unit 133 operates on the basis of the size KN.
• the resource demapping unit 131 of the receiver 121 shown in figure 4 is implemented for demapping the symbols in the time-frequency resource grid back to each transport block. In the embodiment shown in figure 4, the receiver 121 is configured to extract pilot or reference signals at the resource demapping unit 131 for channel estimation using the channel estimation unit 137.
• the (analysis) filter bank 123b of the receiver 121 shown in figure 4 is implemented for de-modulating and matched filtering the signals at the receiver side as well as combining and together with the downsampler 123a downsampling the signals for each subcarrier.
• the analysis filter bank 123b can be based on a frequency spreading structure.
• the symbol demapping unit 129 of the receiver 121 shown in figure 4 is the counterpart of the FEC coding and bit-to-symbol mapping in the transmitter 101 .
• the symbol demapping unit 129 of the receiver 121 shown in figure 4 is the counterpart of the FEC coding and bit-to-symbol mapping in the transmitter 101 .
• the CSI channel state information
• the transmitter 101 can be configured to directly estimate the CSI using uplink-downlink reciprocity, such as in a TDD system. Due to the limited capacity of the feedback channel, it is
• the CSI on a selected subcarrier can be quantized and/or down-sampled by the receiver 121 using, in particular the channel estimation unit 137 and the
• the receiver 121 can be configured to determine a suitable predictor matrix from a codebook on the basis of the CSI and to feed back a predictor matrix indicator (PMI) to the transmitter, as will be described in more detail further below.
• the equalizer 125 of the receiver 121 is configured to use an interpolation based matrix calculation, such as the Laurent polynomial or other transforms, in order to decrease the numerical complexity of deriving the equalization matrix.
• the feedback mechanism implemented between the receiver 121 and the transmitter 101 shown in figures 1 and 4 can have one or more of the following features.
• the CSI is measured by the receiver 121 based on the reference signals extracted from the components provided by the resource demapping unit 131 .
• the CSI can be quantized and downsampled to match a required feedback channel capacity and performance requirement. It is important to note that in this case, the CSI is not averaged and quantized within one processing block (as is done in the prior art), but quantized and/or down-sampled for a selected subcarrier.
• the receiver 121 can be configured to select the precoding matrix indicator (PMI) on the basis of the possibly downsampled CSI.
• PMI precoding matrix indicator
• both the PMI and interpolation parameters can be conveyed from the receiver 121 back to the transmitter 101 via the feedback channel 150a.
• the receiver 121 can be configured to convey interpolation parameters as well as the possibly downsampled CSI to the transmitter 101 .
• the transmitter 101 is configured to select on the basis of the PMI from the receiver 121 the corresponding precoding matrix from the codebook 1 19.
• the transmitter 101 can be configured to interpolate the precoding matrix from the codebook 1 19 in the oversampled frequency domain, i.e. at each sampling point of the plurality of sampling points in the frequency domain, on the basis of the
• the interpolation parameters provided by the receiver 121 can include, in particular, the oversampling factor K used by the receiver 121 .
• the exchange of CSI information between the transmitter 101 and the receiver 121 can be implemented according to the one or more of the embodiments described below.
• the transmitter 101 is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of channel state information associated with the communication channel.
• the transmitter 101 is configured to obtain the channel state information associated with the communication channel 150 on the basis of a pilot signal, which the transmitter 101 has received from the receiver 121 . In another embodiment, the transmitter 101 is configured to obtain the channel state information associated with the communication channel 150 from the receiver 121 , that has been determined by the receiver 121 on the basis of a pilot signal transmitted from the transmitter 101 to the receiver 121 .
• the transmitter 101 is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain by interpolating the channel state information associated with the communication channel 150 at the plurality of sampling points in the frequency domain, for which no channel state information is available, and by determining the precoding matrix per sampling point of the plurality of sampling points in the frequency domain on the basis of the channel state information at the plurality of sampling points in the frequency domain.
• the transmitter 101 is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain by interpolating the channel state information associated with the communication channel 150 at the plurality of sampling points in the frequency domain, for which no channel state information is available, on the basis of the interpolation parameters provided by the receiver 121 .
• the transmitter 101 is configured to determine the precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain on the basis of the precoder matrix indicator provided by the receiver 121 and further configured to determine the precoding matrix at the plurality of sampling points in the frequency domain by selecting a precoding matrix from a predefined set of precoding matrices defined in the codebook 1 19 on the basis of the precoder matrix indicator, wherein each precoding matrix of the predefined set of precoding matrices is defined at the plurality of subcarriers, and by interpolating the selected precoding matrix at the plurality of sampling points in the frequency domain, for which the precoding matrix is not defined.
• the receiver 121 is configured to provide the channel state information associated with the communication channel 150 to the transmitter 101 on the basis of at least one pilot signal from the transmitter 101 , wherein the channel state information allows the transmitter 101 to determine a precoding matrix for precoding the plurality of MCM signals per sampling point of the plurality of sampling points in the frequency domain.
• the receiver 121 is further configured to provide interpolation parameters to the transmitter 101 for interpolating the channel state information associated with the communication channel at the plurality of sampling points in the frequency domain.
• the receiver 121 is configured to determine the precoder matrix indicator on the basis of at least one pilot signal from the transmitter 101 and to provide the precoder matrix indicator to the transmitter 101 allowing the transmitter 101 to determine the precoding matrix per sampling point of the plurality of sampling points in the frequency domain by selecting a precoding matrix from a predefined set of precoding matrices on the basis of the precoder matrix indicator, wherein each precoding matrix of the predefined set of precoding matrices is defined at the plurality of subcarriers, and by interpolating the selected precoding matrix at the plurality of sampling points in the frequency domain, for which the precoding matrix is not defined.
• Interpolation Method apply spherical interpolation to the precoding/equalization matrices at resource blocks in order to obtain precoding/equalization matrix at each sub-bin
• an FBMC-OQAM system with 256 subcarriers has been chosen.
• the user equipped with the receiver 121 according to an embodiment is allocated to a subband of 15 RBs (resource blocks), while each RB consists of 12 subcarriers. Thus, there are 180 used subcarriers.
• K 4
• the signal vector in the oversampling domain consists of 723 tones.
• the performance has been evaluated with respect to the oversampling processing for the equalization. Specifically, given the fixed precoding matrix for each tone at the transmitter 101 and the equalization matrix at each subcarrier, spherical interpolation is performed in this example in order to obtain the equalization matrix for each tone.
• Figure 5 shows the BLER performance of oversampling-based equalization provided by embodiments of the invention for a synchronous transmission scenario.
• FBMC- OQAM both a per-subcarrier (per SC) and a per-frequency-tone (per bin) equalization are performed.
• the state of the art scheme i.e., conventional per-subcarrier equalization for OFDM, is also shown.
• the results validate that per-bin equalization provided by embodiments of the invention outperforms per subcarrier equalization in a scenario with severe frequency selective channels. This can be observed in the performance for the higher order modulation coding scheme (MCS), yielding 2-3 dB gain compared to the conventional per-SC equalization.
• MCS modulation coding scheme
• Figure 6 depicts the BLER performance of oversampling-based equalization provided by embodiments of the invention for the asynchronous transmission.
• two user equipments UEs
• UEs user equipments
• FIG. 6 depicts the BLER performance of oversampling-based equalization provided by embodiments of the invention for the asynchronous transmission.
• two user equipments UEs
• FIG. 6 depicts the BLER performance of oversampling-based equalization provided by embodiments of the invention for the asynchronous transmission.
• two user equipments UEs
• distortions caused by the timing misalignment of the two UEs as well as the corresponding channel frequency selectivity cannot be well-compensated by the conventional per-SC equalization, while this can be effectively achieved by the per-bin equalization as provided by embodiments of the invention.
• embodiments of the invention are generally applicable to MCM schemes.
• embodiments of the invention are remarkably beneficial, as the spectral-spatial domain smoothing is achieved by the continuous phase drift of the interpolated precoder, as exemplified for FBMC/OQAM systems.
• Embodiments of the invention provide, for instance, for the following additional advantages. Since according to embodiments of the invention each tone is precoded and equalized individually, channel variations on each tone can be equalized, leading to a high robustness to high frequency selectivity. By interpolating the precoding matrix in the oversampling domain, inter-block interference at the precoded block boundaries can be completely eliminated. While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application.

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• 2016
  • 2016-03-31 CN CN201680084349.5A patent/CN109076042A/zh active Pending
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