OFDM MODULATOR FOR BLOCK-FILTERED OFDM TRANSMITTER, RELATED BLOCK-FILTERED OFDM TRANSMITTER AND TRANSCEIVER SYSTEM

Abstract

An OFDM modulator including a predistortion module configured to receive the N consecutive data carriers and configured to compensate for distortion subsequently introduced by a polyphase filter bank connectable to the output of the OFDM modulator, a transformation module configured to apply a discrete inverse Fourier transform of constant size N.sub.IDFT independently of the numbering and transmission band used by the OFDM transmitter including the OFDM modulator, a filling module, the input of which is connected to the output of the predistortion module, and the output of which is connected to the input of the transformation module, and configured to insert (N.sub.IDFT−N.sub.c) null carriers in succession to the N.sub.c consecutive data carriers independently of the parity of the index i associated with the OFDM modulator.

Claims

1. An OFDM modulator of a set of M OFDM modulators in parallel with a block filtered OFDM transmitter configured to communicate using a transmission band and a numbering, variable in real time, each OFDM modulator being associated with an index i such that 0≤i≤M−1, M being constant independently of the numbering and transmission band of said transmitter, the block-filtered OFDM transmitter further comprising a serial-to-parallel conversion module upstream of said assembly, configured to convert an incoming serial data stream into N.sub.FFT parallel data carriers, the OFDM modulator being configured to receive a block of& consecutive data carriers of said N.sub.FFT parallel data carriers as input, the OFDM modulator comprising at least one predistortion module configured to receive said N.sub.c consecutive data carriers and configured to compensate for distortion subsequently introduced by a polyphase filter bank of said OFDM transmitter, the output of said OFDM modulator being connectable to the input of the polyphase filter bank wherein the OFDM modulator further comprises: a transformation module configured to apply a discrete inverse Fourier transform IDFT of constant size N.sub.IDFT independently of the numbering and transmission band of said transmitter, a filling module the input of which is connected to the output of the predistortion module, and the output of which is connected to the input of the transformation module, the filling module being configured to insert (N.sub.IDFT−N.sub.c) null carriers in succession to the N.sub.c consecutive data carriers independently of the parity of the index i associated with said OFDM modulator.

2. The OFDM modulator according to claim 1, wherein the OFDM modulator is configured to process the data according to their order of arrival independently of the value of its index i.

3. The OFDM modulator according to claim 1, wherein the OFDM modulator further comprises: a parallel-to-serial conversion module configured to convert the N.sub.IDFT parallel time outputs configured to be output from the transformation module into a serial stream of time samples, and an insertion module, the input of which is configured to be connected to the output of the parallel-serial conversion module, the insertion module being configured to insert a guard time, corresponding to a predetermined number N.sub.cs of additional time samples constant independently of the numbering and the transmission band of said transmitter.

4. The OFDM modulator according to claim 3, wherein the guard time corresponds to a cyclic prefix.

5. The OFDM modulator according to claim 3, wherein the guard time corresponds to a cyclic suffix.

6. The OFDM modulator according to claim 1, wherein the OFDM modulator further comprises a decimation module, located downstream of said transformation module, the decimation module being configured to decimate the time samples obtained from said transformation module by a factor equal to N.sub.IDFT/(2N.sub.c).

7. The OFDM modulator according to claim 1, wherein the OFDM modulator further comprises a spectrum shifting module configured to apply to the samples, in their order of arrival, a rotation in the time domain of value of (−1).sup.i+1π/2, where i is the indexed associated with said OFDM modulator.

8. A block-filtered OFDM transmitter configured to communicate using a variable transmission band and numbering in real time, the OFDM transmitter comprising successively: a serial-to-parallel conversion module configured to convert an incoming serial data stream into N.sub.FFT parallel data carriers, a set of M OFDM modulators in parallel according to claim 1, each OFDM modulator being associated with an index i such that 0≤i≤M−1, M being constant regardless of the numbering and transmission band of said transmitter, each OFDM modulator being configured to receive as input a set of N.sub.c consecutive data carriers of said N.sub.FFT parallel data carriers, the sets of N.sub.c consecutive carriers processed by each modulator being all disjoint, N.sub.FFT being equal to M times N.sub.c, a bank of polyphase filters configured to be connected to the M outputs of said set of M OFDM modulators.

9. The block-filtered OFDM transmitter according to claim 8, wherein the number M of OFDM modulators is reconfigurable.

10. A transceiver comprising a block-filtered OFDM transmitter according to claim 9.

Description

[0048] These features and advantages of the invention will become clearer upon reading the following description, given only as a non-limiting example, and made with reference to the attached drawings, in which:

[0049] FIG. 1 is a schematic representation of a block-filtered OFDM transmitter according to the prior art described above;

[0050] FIG. 2 is a schematic representation of a block-filtered OFDM transmitter according to the present invention;

[0051] FIG. 3 is a schematic representation of the processing implemented by one of the OFDM modulators of the block-filtered OFDM transmitter according to the present invention.

[0052] FIG. 2 is a schematic representation of a block-filtered OFDM transmitter E according to the present invention. More specifically, the block-filtered OFDM transmitter E is configured to communicate using a variable transmission band and numbering in real time, the OFDM transmitter E comprising successively, a serial-to-parallel conversion module 16, as previously illustrated by FIG. 1, configured to convert an incoming serial data stream into N.sub.FFT parallel data carriers, followed, as illustrated by FIG. 2, by a set of M OFDM modulators 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 in parallel, each OFDM modulator being associated with an indexed i such that 0≤i≤M−1, M being constant independently of the numbering and transmission band of said transmitter E, the set of M OFDM modulators 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 in parallel being itself followed by a bank 14 of polyphase filters configured to connect to the M outputs of said set of M OFDM modulators.

[0053] Each OFDM modulator 280, 281, . . . , 28i, . . . , 28.sub.M−1 is configured to receive as input a set of N.sub.c consecutive data carriers of said N.sub.FFT parallel data carriers, the sets of N.sub.c consecutive carriers processed by each modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 being all disjoint, N.sub.FFT being equal to M times N.sub.c.

[0054] More specifically, as illustrated in FIG. 2, each OFDM modulator, in particular OFDM modulator 28.sub.0, includes a predistortion module 30 configured to receive said N.sub.c consecutive data carriers and configured to compensate for distortion subsequently introduced by polyphase filter bank 14 of said E OFDM transmitter, the output of said OFDM modulator being connectable to the input of polyphase filter bank 14.

[0055] Each OFDM modulator, in particular OFDM modulator 280, further comprises a filling module 32, the input of which is connected to the output of predistortion module 30, and the output of which is connected to the input of a transformation module 34 configured to apply a discrete inverse Fourier transform IDFT of constant size N.sub.IDFT independently of the numbering and transmission band of said transmitter. The filling module 32 is configured to insert (N.sub.IDFT−N.sub.c) null carriers (hereinafter referred to as zeros carrying null-valued data) following the N.sub.c consecutive data carriers regardless of the parity of the indexed i associated with said considered OFDM modulator.

[0056] In other words, the filling module 32 is dedicated to inserting zeros, using a unique insertion scheme of (N.sub.IDFT−N.sub.c) zeros, with the zeros inserted after N.sub.c data. Furthermore, the data is processed in its order of arrival independently of the parity of the indexed i associated with said OFDM modulator under consideration, (i.e. regardless of the sub-channel), which solves the flow interruption problem associated with the transmitter architecture previously described in relation to FIG. 1, since each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1, is then conducive to processing the data according to its order of arrival independently of the value of its indexed i.

[0057] Thus, the filling module 32 plays a double role, that is, adding the N.sub.c null carriers, to allow to guarantee the orthogonality principle on the one hand, and on the other hand, filling the input of the discrete inverse Fourier transform IDFT with (N.sub.IDFT−2N.sub.c) zeros (i.e. additional null carriers) to use only one size N.sub.IDFT of discrete inverse Fourier transform IDFT regardless of numbering and transmission band.

[0058] An example of filling zero carriers (i.e. zeros) is illustrated by Table 3 below for a number N.sub.c of data carriers such as N.sub.c=32 and N.sub.c=256 and with a constant size N.sub.IDFT of discrete inverse Fourier transform IDFT such as: N.sub.IDFT=512 regardless of numbering and transmission band.

TABLE-US-00003 TABLE 3 N.sub.c = 32 Carrier number (independently of 0 to 31 32 to 511 the parity of the indexed i associated with said OFDM modulator (i.e. sub-channel)) Data number 0 to 31 Inserted zeros N.sub.c = 256 Carrier number (independently of 0 to 255 256 to 511 the parity of indexed i associated with said OFDM modulator (i.e. sub-channel)) Data number 0 to 255 Inserted zeros

[0059] The transformation module 34 configured to apply a discrete inverse Fourier transform IDFT is, according to the present invention, configured to perform an IDFT of constant size N.sub.IDFT (regardless of numbering and band). The zero-filling implemented by the filling module 32 at the input of the discrete inverse Fourier transform IDFT (frequency domain) corresponds to an oversampling of the signal in the time domain by a factor equal to: N.sub.IDFT/(2N.sub.c).

[0060] Each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 further comprises, as illustrated in FIG. 2, a parallel-to-serial conversion module 36 configured to convert the N.sub.IDFT parallel time outputs configured to output from the transformation module 34 into a serial stream of time samples.

[0061] Furthermore, each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 further comprises an insertion module 38, the input of which is suitable to be connected to the output of the parallel-to-serial conversion module 36, the insertion module 38 being configured to insert a guard time, corresponding to a predetermined number N.sub.cs of additional temporal samples constant independently of the numbering and the transmission band of said transmitter E.

[0062] According to a first variant, the guard time corresponds to a cyclic prefix.

[0063] According to a second variant, the guard time corresponds to a cyclic suffix.

[0064] Furthermore, each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 further comprises a decimation module 40, located downstream of said transformation module 34, the decimation module 40 being configured to decimate the time samples obtained from said transformation module 34 by the factor equal to N.sub.IDFT/(2N.sub.c). Such decimation allows the desired timing to be recovered.

[0065] Examples of decimation for a constant size N.sub.IDFT of discrete inverse Fourier transform IDFT such as: N.sub.IDFT=512 or N.sub.IDFT=1024 regardless of numbering and transmission band are illustrated in particular by table 4 below.

TABLE-US-00004 TABLE 4 N.sub.c Number of zeros N.sub.IDFT Decimation 32 480 512 8 64 448 4 128 384 2 256 256 None 64 960 1024 8 128 896 4 256 768 2 512 512 None

[0066] In addition, each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 further comprises a spectrum shifting module 42 configured to apply a time domain rotation of value (−1).sup.i+1π/2 to the samples, in their arrival order, with i the indexed associated with said OFDM modulator.

[0067] Such a spectrum shifting module 42 (i.e., time domain rotation module 42) associated with the previously described filling module 32, enables reproduction of the formatting, as illustrated in FIG. 3, at the output of each OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 according to the present invention, examples of which are indicated in Table 1, with the major difference that the proposed modulator architecture according to the present invention does not require any data flow interruption.

[0068] More precisely, in FIG. 3, for a number N.sub.c of data carriers such that N.sub.c=128, as illustrated by representation 44, and with a constant size N.sub.IDFT of discrete inverse Fourier transform IDFT such that: N.sub.IDFT=512 regardless of numbering and transmission band implemented by the transformation module 34, the filling module 32 inserts a number of null carriers equal to 512−128=384, following the N.sub.c=128 consecutive data carriers, independently of the parity of the indexed i associated with said OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1, as illustrated by representation 46.

[0069] Then, as illustrated by representation 48 of FIG. 3, the decimation processing implemented by the decimation module 40 in the time domain, returns to the reduction of the spectrum in the frequency domain by a factor of two, to obtain 256 carriers with always N.sub.c first consecutive data carriers such that N.sub.c=128 and 128 following null carriers.

[0070] The processing implemented by the spectrum shifting module 42 is illustrated by the frequency domain representations 50 and 52 for an even indexed i OFDM (i.e. subchannel) modulator, and 54 and 56 for an odd indexed i OFDM (i.e., subchannel) modulator.

[0071] Specifically, the spectrum shifting module 42 implements a rotation in the time domain of value (−1).sup.i+1π/2, with i the indexed associated with said OFDM modulator, so that for an even indexed i, such a rotation in the time domain amounts to distributing, as illustrated by embodiments 50 and 52, in the frequency domain, the N.sub.c data carriers on the sides of the spectrum with 128 null carriers in the middle of the spectrum, the first N.sub.c/2=64 data (represented with a dashed texture) of the incoming stream being placed at the end of the spectrum, while the next N.sub.c/2=64 data (represented with a diagonal texture) of the incoming stream being placed at the beginning of the spectrum with null carriers in the middle of the spectrum. For an odd indexed i, such a rotation in the time domain amounts to distributing, as shown in representations 54 and 56, in the frequency domain the N.sub.c data carriers in the center of the spectrum with null carriers on the sides.

[0072] In other words, avoiding an interruption of the data stream, the right or left shift of the spectrum according to the subchannel indexed parity is controlled, according to the present invention, simply by the sign of the rotation implemented by the spectrum shifting module 42. This spectrum shifting module 42 uses the property that a rotation in the time domain is equivalent to a spectral shift.

[0073] With the architecture of the transmitter E proposed according to the present invention, the various parameterizations of the LF-OFDM transmitter considering a constant number M of OFDM modulators (i.e. subchannels), the width of which evolves with the bandwidth B of the transmission band, become the parameterizations illustrated by table 5 presented below, with a transmission band and a numbering μ={0, 1, 2, 3} (number associated with a predetermined value of the inter-carrier space Δf) both able to vary respectively and independently in real time:

TABLE-US-00005 TABLE 5 Band = 50 MHz Band = 100 MHz Band = 200 MHz N.sub.cΔf = 3.84 MHz N.sub.cΔf = 7.68 MHz N.sub.cΔf = 15.36 MHz Δf IDFT IDFT IDFT μ (kHz) N.sub.c Size N.sub.cs N.sub.c Size N.sub.cs N.sub.c Size N.sub.cs 0 15 256 2048 128 512 2048 128 1024 2048 128 1 30 128 256 512 2 60 64 128 256 3 120 32 64 128

[0074] In comparison with Table 2 presented in relation to the prior art, the architecture of the E transmitter according to the present invention, regardless of numbering and band, is therefore characterized by both a single discrete inverse Fourier transform size IDFT (N.sub.IDFT) and a single guard interval size N.sub.cs used.

[0075] The architecture of the transmitter E according to the present invention thus allows for simplification of the alternation of the position of the zeros during the formatting implemented according to the state of the art, thanks to the filling module 32 previously described, completed by the action in the time domain of the decimation module 40 and the spectrum shifting module 42 (or even rotation module in the time domain). The insertion of zeros (i.e. zero carriers), implemented by the filling module 32, no longer requires any indexing operation according to the sub-channel parity and does not require interrupting the data flow.

[0076] The person skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, as the above-mentioned embodiments and variants are suitable to be combined with each other to generate new embodiments of the invention.

[0077] In particular, the OFDM modulator architecture 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 proposed in FIG. 2, applies for any M value: the system designers choose M according to their own objectives. In other words, the number M of OFDM modulators 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1 is reconfigurable, this parameter M having an influence on the size of the filter bank 14 and on the size of the Fast Fourier Transform (FFT) of the receiver of a transceiver system, not shown, comprising a block-filtered OFDM transmitter E according to the present invention. The width M of the subchannels (i.e. OFDM modulator 28.sub.0, 28.sub.1, . . . , 28.sub.i, . . . , 28.sub.M−1) is a parameter of the OFDM E-transmitter suitable for development, such development being supported by the invention.

[0078] The present invention thus proposes an E OFDM transmitter architecture, in particular compatible with version 15 of the 3GPP standard, 5G NR, which makes it likely to be used by any system claiming this standard, in particular so-called “multi-service” systems, mixing services with different requirements in the same frame, particularly suitable for using BF-OFDM.