Methods and apparatuses for multiple access in a wireless communication network using DCT-OFDM
The present invention provides an advantageous transmitter apparatus and associated method, for generating a Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal for transmission. These transmit-side innovations include circuit configuration and signal processing methods for mapping Ku “input subcarriers” to N “output subcarriers,” where the “output subcarriers” are some or all of the subcarriers defined for the SC-DCT OFDM signal. In one or more embodiments, Ku is less than N, and the mapping is based on advantageous DCT/IDCT precoding. The present invention additionally or alternatively includes advantageous frequency-selective mapping, and further provides a corresponding receiver apparatus and associated method, for receiving and de-mapping the SC-DCT OFDM signals contemplated herein.
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This application is a continuation of U.S. patent application Ser. No. 12/913,119, filed on Oct. 27, 2010, now U.S. Pat. No. 8,693,571, which claims priority to U.S. Provisional Patent Application No. 61/313,346 filed on Mar. 12, 2010, all of which are hereby incorporated by reference herein in their entirety.
FIELD OF THE INVENTIONThe present invention generally relates to wireless communication networks, and particularly relates to methods and apparatuses providing multiple-access in wireless communication networks based on DCT-OFDM (Discrete Cosine Transform Orthogonal Frequency Division Multiplex).
BACKGROUNDOFDM based on Discrete Fourier Transform (DFT) processing is a popular modulation approach in developing and planned wireless communication systems, such as 3GPP LTE, IEEE WiMAX 802.16x, IEEE WiFi 802.11x, etc. DFT-based modulation provides efficient and practical channel equalization algorithms, when used for the transmission of multi-carrier signals, like the OFDM signals used in LTE and LTE-Advanced. Furthermore, multiple access solutions that allow flexible resource allocation (e.g., Orthogonal Frequency Division Multiple Access or OFDMA) can be implemented in conjunction with the use of DFT-based and other OFDM signals structures.
However, the OFDM signal is characterized by large fluctuations of its power envelope that result in occasional spikes in the power of the signal—for example, such signals are characterized by having a relatively high Peak-to-Average-Power-Ratio (PAPR) or high “Cubic Metric” (CM). The large power fluctuations in high PAPR/CM signals impose significant design requirements on the radiofrequency (RF) power amplifier (amplifier chains) used to transmit OFDM signals. In particular, the large power fluctuations require the RF Pas to be operated with significant back-off, to have sufficient margin for accommodating the power peaks in the OFDM signal. More generally, the overall transmit signal chain must be “dimensioned” in one or more senses, to handle the worst-case power peaks of the OFDM signal.
For energy, cost, or space critical designs (e.g., mobile devices) the power back-off margins required by DFT-OFDM lead to an inefficient solution. Therefore, modifications to the standard OFDM system have been introduced, to obtain systems with roughly the same advantages of DFT-OFDM over single carrier systems, but with more compressed signal dynamics. The two most popular techniques are Distributed Single Carrier OFDMA (sometimes also called B-IFDMA) and Localized Single Carrier (LOC-SC) OFDMA, also referred to as DFTS-OFDM. LOC-SC-OFDMA has been adopted for 3GPP LTE, to improve the efficiency of uplink transmissions.
In both LOC/DIST-SC-OFDMA, the Inverse DFT (IDFT) modulator at the transmitter is preceded by a standard DFT precoder. The two techniques differ in the way the outputs from the DFT precoder are mapped to the inputs on the IDFT. Inverse processing is correspondingly performed at the receiver side, and linear equalization techniques can be performed in the same way as for conventional OFDM/OFDMA. As a further alternative, researchers have investigated new modulation systems based on the use of Discrete Cosine Transform (DCT) processing. See, e.g., P. Tang, N. C. Beaulieu, “A Comparison of DCT-Based OFDM and DFT-Based OFDM in Frequency Offset and Fading Channels,” IEEE 2006.
Further work has touched on the use of DCT-based transmission “precoding” in the OFDM context, in the interest of improving system performance through, e.g., lower Bit Error Rates (BERs). See, e.g., de Fein, C. and Fagan, A. D., “Precoded OFDM—An Idea Whose Time Has Come,” ISSC 2004, Belfast. Additional work on precoding in the context of DCT-based OFDM appears in, e.g., Wang, Zhengdao and Giannakis, Georgios, “Linearly Precoded or Coded OFDM against Wireless Channel Fades?” Third IEEE Signals Processing Workshop, Taiwan, 2001.
Broadly, with DCT-based OFDM, the transmitter employs a DCT (or, equivalently, an IDCT) for modulation processing. Compared to conventional DFT-based OFDM systems equalization in the DCT-OFDM context is more complex. However, DCT-based OFDM systems retain the attractive channel diagonalization properties of DFT-OFDM, based on employing a symmetric Cyclic Prefix (CP) and a pre-filter at the receiver. See, e.g., N. Al-Dhahir, H. Minn, S. Satish, “Optimum DCT-Based Multicarrier Transceivers for Frequency-Selective Channels,” IEEE 2006.
While DCT-based OFDM offers a number of promising characteristics, the underlying signals used in an a DCT-OFDM system still experience potentially large envelope fluctuations that are difficult to handle within the practical limits of hardware. Furthermore, there appears to be significant work remaining in developing efficient multiple access techniques that allow the co-scheduling of multiple users, while still offering an advantageously low PAPR/CM.
SUMMARYThe present invention provides an advantageous transmitter apparatus and associated method, for generating a Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal for transmission. These transmit-side innovations include circuit configuration and signal processing methods for mapping Ku “input subcarriers” to N “output subcarriers,” where the “output subcarriers” are some or all of the subcarriers defined for the SC-DCT OFDM signal. In one or more embodiments, Ku is less than N, and the mapping is based on advantageous DCT/IDCT precoding. The present invention additionally or alternatively includes advantageous frequency-selective mapping, and further provides a corresponding receiver apparatus and associated method, for receiving and de-mapping the SC-DCT OFDM signals contemplated herein.
In one embodiment, the present invention provides a transmitter circuit configured to generate an SC-DCT OFDM signal for transmission. The transmitter circuit includes a signal processing chain configured to map Ku input subcarriers to N output subcarriers, according to the formula N=2SKu. Here, S indicates the integer number of DCT precoder stages included in series within the signal processing chain, where S≥1.
The signal processing chain of the transmitter circuit includes: a serial-to-parallel converter configured to generate the Ku input subcarriers according to a series of information symbols to be transmitted; a cyclic prefix or zero padding circuit configured to add a cyclic prefix or zero padding to the N output subcarriers, for input to a parallel-to-serial converter that is configured to form the SC-DCT OFDM signal; and one or more series DCT precoder stages between the serial-to-parallel converter and the cyclic prefix or a zero padding circuit.
Each such DCT precoder stage is configured to generate 2M output subcarriers from M input subcarriers, and to map the M input subcarriers to even-numbered or odd-numbered ones of the 2M output subcarriers, in dependence on an even/odd shift control signal applied to the stage, and each such stage comprising a DCT circuit followed by an IDCT circuit. Further, a first one of the DCT precoder stages takes the Ku subcarriers as its M input subcarriers, and a last one of the DCT precoder stages provides the N output subcarriers as its 2M output subcarriers.
In another embodiment, the present invention provides a method of generating an SC-DCT OFDM signal for transmission. The method includes forming a parallel vector of Ku input subcarriers from a series of information symbols to be transmitted, and mapping the Ku input subcarriers to N output subcarriers by passing the Ku input subcarriers through one or more DCT precoder stages. Here, N=2SKu, and S (S≥1) indicates the integer number of series DCT precoder stages. Further, the method includes inserting a cyclic prefix or a zero padding into the N output subcarriers and subsequently converting the N output subcarriers into a serial signal, for generating the SC-DCT OFDM signal for transmission.
As for mapping according to the method, the mapping done in each DCT precoder stage comprises passing M input subcarriers through a DCT function followed by an IDCT function, to generate 2M output subcarriers. The M input subcarriers are mapped to even or odd ones of the 2M output subcarriers, in dependence on an even/odd shift control signal. In this regard, M=Ku for a first DCT precoder stage and 2M=N for a last DCT precoder stage.
In a further embodiment, the present invention provides a method of generating an SC-DCT OFDM signal for transmission, where the method includes forming a parallel vector of Ku input subcarriers from a series of information symbols to be transmitted, and mapping the Ku input subcarriers to N output subcarriers. That mapping is accomplished by passing the Ku input subcarriers through a mapping circuit and an Inverse (IDCT) circuit of size N, wherein Ku<N.
In particular, the Ku subcarriers are mapped on a frequency-selective basis to said N output subcarriers, based on identifying preferred subcarrier frequencies. For example, channel state information from a remote receiver targeted by the SC-DCT OFDM signal can be used to guide the frequency-selective mapping, such as to select those subcarriers having more favorable fading and/or interference characteristics. The method further includes inserting a cyclic prefix or a zero padding into the N output subcarriers and subsequently converting the N output subcarriers into a serial signal, for generating the SC-DCT OFDM signal for transmission.
In yet another embodiment, the present invention provides a receiver circuit configured to process a received SC-DCT OFDM signal. The receiver circuit includes a signal processing chain configured to de-map N input subcarriers from the received SC-DCT OFDM signal to Ku output subcarriers, according to the formula Ku=N/2S, wherein S indicates the integer number of DCT decoder stages included in series within the signal processing chain. (Note that S≥1.) The signal processing chain also includes a pre-processing circuit that is configured to remove a cyclic prefix from the N input subcarriers, in advance of the de-mapping.
As part of its decoding configuration, the signal processing chain includes one or more series DCT decoder stages following the pre-processing circuit. Each such stage is configured to generate M output subcarriers from 2M input subcarriers, by mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers, in dependence on an even/odd shift control signal applied to the stage. In accordance with this configuration, each DCT decoder stage comprises a DCT circuit followed by an IDCT circuit. Thus, a first one of the DCT decoder stages takes the N input subcarriers as its 2M input subcarriers, and a last one of the DCT decoder stages provides the Ku output subcarriers as its M output subcarriers.
Still further, in another embodiment the present invention provides a method for use in a receiver circuit configured to process a received SC-DCT OFDM signal. The method includes removing a cyclic prefix from N input subcarriers from the received SC-DCT OFDM signal, and de-mapping the N input subcarriers from the received SC-DCT OFDM signal to Ku output subcarriers, after removing said cyclic prefix, according to the formula Ku=N/2S. Here, S indicates the integer number of DCT decoder stages included in series within a signal processing chain of the receiver circuit, where S≥1.
According to the method, the de-mapping includes, in each of one or more series DCT decoder stages included in the receiver circuit, generating M output subcarriers from 2M input subcarriers, based on mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers, in dependence on a an even/odd shift control signal applied to the stage, and further comprising generating said M output carriers based on performing a DCT on the 2M input subcarriers, followed by performing an IDCT on the results obtained from said DCT.
Further, while this disclosure uses LTE Advanced as an example context, it should be understood that the present invention has broader applicability. For example, the present invention has applicability to future evolutions of other systems, including WCDMA, CDMA, WiMax, UMB, etc. More generally, the present invention is not limited to the above brief summary of features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
As part of the signal processing carried out in the system of
With the above DCT structure in mind,
In
Note that the other subcarriers are, in at least one embodiment, assigned zero (“0”) or no-signal values. Thus, where the radio apparatus 10 is one of multiple user terminals or other devices transmitting on the uplink (UL) to the radio apparatus 20 serving as a network base station, it will be understood that different such devices may use different Ku subsets of the N available subcarriers. Thus, the set of selected Ku subcarriers used by a given user is, according to one or more embodiments taught herein, assigned by a scheduling function. For example, by properly choosing the scheduled subcarriers it is possible to focus the signal energy on the most convenient or favorable portions of the wireless channel, i.e., typically the subcarrier where the channel has large energy.
The illustrated transmit signal processing chain 30 includes, beyond the S/P converter 32, a mapping circuit 34 that maps the Ku subcarriers to particular ones of the N subcarriers of the OFDM signal—in this context, the Ku subcarriers are referred to as “input” subcarriers, as they are the ones being mapped, and the N subcarriers are referred to as the “output” subcarriers, as they are the actual subcarriers available for use in the transmitted OFDM signal.
In any case, the mapping circuit 34 is followed by an IDCT circuit 36 (of size N), which applies an Inverse Discrete Cosine Transform to the Ku subcarriers. The size N output from the IDCT circuit 36 includes the mapped Ku subcarriers with the remaining (N−Ku) subcarriers set, e.g., to zero. A CP/ZP circuit 38 inserts a cyclic prefix (CP) or a zero padding (ZP). Note that at least one embodiment of the CP/ZP circuit 38 adds a CP and, optionally, a cyclic suffix (CS). Also, note that certain design issues may be considered in terms of deciding whether to use CP insertion or ZP insertion. For example, CP insertion effectively diagonalizes the propagation channel and thereby simplifies equalization processing at the receiver, although prefiltering generally is required. In contrast, equalization is more complex when ZP is used, but prefiltering generally is not needed.
After CP or ZP insertion, a parallel-to-serial (P/S) converter 40 converts the signal to a serial stream. The serial stream is input to the OFDM transmitter circuit 14, for D/A conversion, modulation to the carrier/subcarrier frequencies, amplification, etc., and transmission as the SC-DCT OFDM signal.
Thus, one method taught herein is the generation of an SC-DCT OFDM signal for transmission, based on: forming a parallel vector of Ku input subcarriers from a series of information symbols to be transmitted; and mapping the Ku input subcarriers to N output subcarriers through a mapping circuit 34 and an Inverse DCT (IDCT) circuit 36 of size N, wherein N>Ku. In particular, wherein the mapping is performed on a frequency-selective basis, based on identifying preferred subcarrier frequencies. That is, the IDCT circuit 36 maps the Ku parallel information symbols to the inputs of the IDCT circuit 36, which produces N output subcarriers.
On the receive-side, one sees an example receive signal processing chain 50, which, for example, is implemented within the receiver processing circuits 22 that are depicted for the second radio apparatus 20 in
The receive signal processing chain further includes a CP/ZP removal circuit 52, which also may be configured as a prefilter; a size N DCT circuit 54; a demapping circuit 56, to de-map the Ku subcarriers of interest from the N subcarriers; an equalization (EQ) circuit 58 to operate on the Ku subcarriers; and a parallel-to-serial (P/S) converter 60, to output a serialized version of the equalized signal from the EQ circuit 58. It will be understood that a base station or other node intended for receiving and processing signals from multiple remote transmitters will include (at least functionally) multiple receive signal processing chains 50, for processing the signals from different transmitters. Alternatively, the receive signal processing chain 50 can be sized or otherwise structured to process multiple sets of Ku subcarriers from the received SC-DCT OFDM signal.
In at least one embodiment, a method of generating a LOC-SC-DCT OFDM signal for transmission comprises converting a number Ku of information symbols into a parallel vector of Ku information symbols, and precoding the parallel Ku information symbols in a Discrete Cosine Transform (DCT) precoder, to create Ku precoded information symbols. The method further includes mapping the Ku precoded information symbols to Ku selected inputs of an Inverse DCT (IDCT) modulator and correspondingly generating Ku mapped subcarriers from among N output subcarriers from the IDCT modulator. Still further, the method includes inserting a cyclic prefix (CP) or a zero padding (ZP) into the N subcarriers, and converting the N subcarriers into a serial stream for transmission as the LOC-SC-DCT signal. Note that in at least one such embodiment, generating the Ku mapped subcarriers from among N output subcarriers from the IDCT modulator comprises generating Ku consecutively-mapped subcarriers from among N output subcarriers from the IDCT modulator.
Such transmit-side precoding results in the receive signal processing chain 50 including an extra component, as compared to the embodiment of
The illustrated receive signal processing chain 50 further includes a CP/ZP removal circuit 52. If the CP/ZP insertion circuit 38 of the transmit signal processing chain 30 is configured to insert a CP, then the CP/ZP removal circuit 52 is configured to remove the CP from the received signal. Conversely, if the CP/ZP insertion circuit 38 is configured to use zero padding—i.e., to insert a ZP rather than a CP—then the CP/ZP removal circuit 52 is configured to remove the ZP from the received signal.
As earlier noted, one advantage of CP insertion on the transmit side is the advantage of simpler equalization on the receive side. That advantage is partially offset by the need for pre-filtering of the received signal when CP insertion is used. Thus, the receive signal processing chain 50 illustrates a pre-filter circuit 53, which is used/implemented in the case that CP insertion is used on the transmit side. In such configurations, the pre-filter circuit 53 is configured to provide the necessary received signal pre-filtering. If ZP insertion is used on the transmit side, pre-filtering need not be implemented.
Following the CP/ZP removal and (possible) pre-filtering, one sees a series of DCT decoder stages 64. In general, the receive signal processing chain 50 includes the same number of DCT decoder stages 64 as DCT precoder stages 44 used in the transmit signal processing chain 30. Here, one sees DCT decoder stages 64-1 through 64-r, corresponding to DCT precoder stages 44-1 through 44-r on the transmit side. Also, note that the first DCT decoder stage 64-1 generally includes an EQ circuit 65, such as depicted in
The use of CP insertion on the transmit side provides channel diagonalization and attendant simplification of the equalization processing implemented in the eq. circuit 65, while the use of ZP generally requires more complex equalization process, while advantageously eliminating the need for pre-filtering. In any case, those of ordinary skill in the art will appreciate that the eq. circuit 65 may be configured to implement an equalization matrix and processing circuit that forms linear combinations of the input (received signal), where the resultant combined (signals) exhibit reduced inter-carrier interference.
In the embodiment of
Each DCT precoding stage 44 on the transmit side doubles the number of generated subcarriers and maps the signal only on even or odd subcarriers according to a SHIFT(s)={0;1} flag, where s is the precoder index. Therefore, only the subcarriers indexed as offset+k*2S (with k=0 . . . Ku; offset={0 . . . −2S−1}) carry the transmitted signal, while the other subcarriers do not carry energy. The value of the variable offset is determined by the values of SHIFT(s). Corresponding decoding steps are performed at the receiver side, where, as noted, the first DCT decoder stage 64-1 includes or is associated with equalization processing, as provided by the eq. circuit 65.
Each DCT precoder stage 44 (and corresponding DCT decoder stage 64) is obtained from a combination of down-sampled DCT/IDCT processing and subcarrier mapping, as shown in
Further, the switches 74/76 in
The embodiment of
Further, with the embodiment of
The method 700 continues with mapping the Ku input subcarriers to N output subcarriers, wherein the mapping is performed in one or more DCT precoder stages (Block 704). Here, the “output” subcarriers represent the actual subcarriers available for use in the SC-DCT OFDM transmit signal to be generated. Thus, the process takes an ongoing serial transmit information stream and converts it into a succession of symbol vectors, each having Ku information symbols, and where each such symbol vector is referred to as Ku “input subcarriers.” In turn, those Ku input subcarriers are mapped to N particular ones of the actual subcarriers comprising the OFDM signal structure.
In particular, the mapping is done using advantageously constructed and configured DCT precoders, as will be detailed later herein. The method continues with inserting a CP or ZP and converting the N output subcarriers to serial form, which is then amplified, etc., and transmitted as the SC-DCT OFDM signal (Block 706).
The method continues with de-mapping the N input subcarriers from the received SC-DCT OFDM signal to Ku output subcarriers, after removing said CP or ZP (Block 804). The de-mapping is done according to the formula Ku=N/2S, where S indicates the integer number of DCT decoder stages included in series within a signal processing chain of the receiver circuit 22 (S≥1). The contemplated de-mapping includes, in each of one or more series DCT decoder stages included in the receiver circuits 22, generating M output subcarriers from 2M input subcarriers.
In particular, such processing is based on mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers, in dependence on a an even/odd shift control signal applied to the stage, and further comprising generating said M output carriers based on performing a DCT on the 2M input subcarriers, followed by performing an IDCT on the results obtained from said DCT. In any case, the method continues with further received signal processing (Block 806), such as decoding or otherwise extracting the originally-transmitted information symbols, for data or control processing at the radio apparatus 20.
Accordingly, in one embodiment, the present invention comprises a transmitter circuit (e.g., transmitter processing circuits 12) configured to generate an SC-DCT OFDM signal for transmission. The transmitter circuit includes a signal processing chain 30 configured to map Ku input subcarriers to N output subcarriers, according to the formula N=2SKu. The term S indicates the integer number of DCT precoder stages 44 included in series within the signal processing chain 30, wherein S≥1.
The signal processing chain 30 includes a serial-to-parallel converter 32 configured to receive a series of Ku information symbols and to correspondingly generate a parallel set of Ku output information symbols—e.g., a vector of Ku output information symbols, for transmission. A CP/ZP circuit 38 is configured to add a CP or ZP to the N output subcarriers, for input to a parallel-to-serial (P/S) converter 40 that is configured to form the SC-DCT OFDM signal. Further, as noted, the signal processing chain 30 further includes one or more series DCT precoder stages 44 between the serial-to-parallel converter 32 and the CP/ZP circuit 38.
Each such stage 44 is configured to generate 2M output subcarriers from M input subcarriers, and to map the M input subcarriers to even-numbered or odd-numbered ones of the 2M output subcarriers, in dependence on an even/odd shift control signal applied to the stage 44. (The transmit processing circuits 12 will be understood to include, for example, a shift control circuit configured to generate the shift control signals.) Further, as shown in
In at least one embodiment, there is a plurality of said signal processing chains 30, each associated with different series of information symbols to be transmitted, and a shift control circuit that is configured to generate even/odd shift control signals for each said signal processing chain 30, such that different patterns of even or odd subcarrier mapping are used between the different signal processing chains 30. In at least one such embodiment, the shift control circuit is configured to generate the different patterns of even or odd subcarrier mapping in consideration of the number of DCT precoder stages 44 included in each signal processing chain 30.
Further, in at least one such embodiment, the shift control circuit is included in a multiple-access scheduling circuit—which, again, is implemented functionally within the transmit processing circuits 12, in one or more example embodiments—that is configured to determine the number of subcarriers allocated to different users, and to control the shifting behaviors of each corresponding signal processing chain 30, to differentiate between the different users.
Accordingly, a method is taught herein comprising mapping a plurality of different sets of Ku input subcarriers according to different even/odd shift control signals having different patterns of even/odd shifting, to differentiate the different sets of Ku input subcarriers. In particular, in one embodiment, the method includes generating the different even/odd shift control signals as part of a multiple-access scheduling method that uses the different patterns of even/odd shifting to differentiate between individual receivers—e.g., multiple radio apparatuses 12 10 —being targeted by SC-DCT OFDM signal transmissions.
Still further, in at least one embodiment, at least one DCT precoder stage 44 in the signal processing chain 30 comprises a direct-mapping DCT precoder stage 44 that is configured to form the 2M output subcarriers by taking the M input subcarriers as a length-M ordered sequence and outputting a length-2M output vector that includes the original ordered sequence interspersed with a time-reversed and mirrored version of the original ordered sequence. Such direct-mapping is based on, for example, the direct-mapping DCT precoder stage 44 being configured to negate or not negate the time-reversed mirrored version of the original ordered sequence included in the length-2M output vector, in dependence on the even/odd shift control signal applied to the direct-mapping DCT precoder stage 44.
Likewise, referring again to
Further, the signal processing chain 50 further includes the previously mentioned one or more series DCT decoder stages 64 following the pre-processing circuit 52. Each such stage 64 is configured to generate M output subcarriers from 2M input subcarriers, by mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers. Such mapping is performed in dependence on a an even/odd shift control signal applied to the stage 64, and each such stage 64 comprises a DCT circuit 80 followed by an IDCT circuit 82 (such as is shown in the example of
In at least one such embodiment, at least one of the DCT decoder stages 64 in the signal processing chain comprises a direct-mapping DCT decoder stage that is configured to form the M output subcarriers by selecting a length-M ordered sequence from the 2M input subcarriers, which are known to be formed as a length-2M ordered sequence the length-M ordered sequence interspersed with a time-reversed and mirrored version of the length-M ordered sequence.
Also, regardless of whether direct mapping is or is not used, at least one embodiment of the receiver circuit includes a parallel-to-serial converter circuit 60 that is configured to convert the Ku output subcarriers into a corresponding serial stream, and a processing circuit (e.g., within the receive processing circuits 22) that is configured to obtain or otherwise process the information symbols of interest from the serial stream. Such symbols represent data and/or control signaling.
As for example details of the above direct mapping, the present invention advantageously recognizes that certain properties of the DIST-SC-DCT-OFDM scheme can be exploited in the implementation of the DCT precoder and decoder stages 44 and 64, respectively. In particular, it is contemplated herein that the DCT precoder and decoder stages 44 and 64 may be implemented in such a way as to avoid explicit calculations of the DCT/IDCT. Notably, the thus-avoided DCT/IDCT computations may well be the most computationally intensive operations at the transmitter or receiver. The alternative (“direct”) implementations of the DCT precoder and decoder stages 44 and 64 are shown in
With the above examples in mind, those skilled in the art will appreciate that the present invention provides a number of advantages. Those advantages include these non-limiting examples: (1) an effective multiple access method that trades scheduling flexibility for signal dynamics compression and where, even in case of full bandwidth allocation, the embodiments of
With these example advantages in mind,
Correspondingly,
To that end, the device 110 includes communication and control circuits 112 (e.g., fixed or programmable digital processing circuitry), including transmitter/receiver processing and control circuits 114, which are associated with transceiver circuits 116 that include one or more receiver signal processing chains 118. These chains 118 are, for example, implemented like the receive signal processing chain 50 depicted in
Note, too, that in keeping with the MA techniques described herein, the device 110 may control or otherwise configure multiple devices 90 to use different even/odd shift patterns in the DCT precoder stages 44 included in their transmit signal processing chains 98. The assignment of different shifting patterns to different devices 90 reduces interference between the SC-DCT OFDM signals transmitted on the shared uplink by those devices 90.
Of course, the example illustrations of
Claims
1. A transmitter circuit configured to generate a Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal for transmission, said transmitter circuit comprising:
- a signal processing chain configured to map Ku input subcarriers to N output subcarriers, according to the formula N=2SKu, wherein S indicates the integer number of DCT precoder stages included in series within the signal processing chain, wherein S≥1, and wherein said signal processing chain includes a serial-to-parallel converter configured to generate the Ku input subcarriers according to a series of information symbols to be transmitted, a prefix or padding circuit configured to add a cyclic prefix or a zero padding to the N output subcarriers, for input to a parallel-to-serial converter that is configured to form the SC-DCT OFDM signal; and
- wherein said signal processing chain further includes one or more series DCT precoder stages between the serial-to-parallel converter and the prefix or padding circuit, each such stage configured to generate 2M output subcarriers from M input subcarriers, and to map the M input subcarriers to even-numbered or odd-numbered ones of the 2M output subcarriers, in dependence on a an even/odd shift control signal applied to the stage, and each such stage comprising a DCT circuit followed by an IDCT circuit; and
- wherein a first one of the DCT precoder stages takes the Ku subcarriers as its M input subcarriers, and a last one of the DCT precoder stages provides the N output subcarriers as its 2M output subcarriers.
2. The transmitter circuit of claim 1, wherein there is a plurality of said signal processing chains, each associated with different series of information symbols to be transmitted, and a shift control circuit that is configured to generate even/odd shift control signals for each said signal processing chain, such that orthogonal patterns of even or odd subcarrier mapping are used between the different signal processing chains.
3. The transmitter circuit of claim 1, wherein at least one DCT precoder stage in the signal processing chain comprises a direct-mapping DCT precoder stage that is configured to form the 2M output subcarriers by taking the M input subcarriers as a length-M ordered sequence and outputting a length-2M output vector that includes the original ordered sequence interspersed with a time-reversed and mirrored version of the original ordered sequence.
4. The transmitter circuit of claim 1, wherein S>1.
5. The transmitter circuit of claim 2, wherein the shift control circuit is configured to generate the different patterns of even or odd subcarrier mapping in consideration of the number of DCT precoder stages included in each signal processing chain.
6. The transmitter circuit of claim 2, wherein the shift control circuit is included in a multiple-access scheduling circuit that is configured to determine the number of subcarriers allocated to different users, and to control the shifting behaviors of each corresponding signal processing chain, to differentiate between the different users.
7. The transmitter circuit of claim 3, wherein the direct-mapping DCT precoder stage is configured to negate or not negate the time-reversed mirrored version of the original ordered sequence included in the length-2M output vector, in dependence on the even/odd shift control signal applied to the direct-mapping DCT precoder stage.
8. A method of generating a Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal for transmission, said method comprising:
- forming a parallel vector of Ku input subcarriers from a series of information symbols to be transmitted;
- mapping the Ku input subcarriers to N output subcarriers by passing the Ku input subcarriers through one or more DCT precoder stages, wherein N=2SKu, and S (S≥1) indicates the integer number of series DCT precoder stages; and
- inserting a cyclic prefix or a zero padding into the N output subcarriers and subsequently converting the N output subcarriers into a serial signal, for generating the SC-DCT OFDM signal for transmission; and
- wherein mapping in each DCT precoder stage comprises passing M input subcarriers through a DCT function followed by an IDCT function, to generate 2M output subcarriers, wherein the M input subcarriers are mapped to even or odd ones of the 2M output subcarriers, in dependence on a an even/odd shift control signal, and further wherein M=Ku for a first DCT precoder stage and 2M=N for a last DCT precoder stage.
9. The method of claim 8, further comprising mapping a plurality of different sets of Ku input subcarriers according to different even/odd shift control signals having different patterns of even/odd shifting, to differentiate the different sets of Ku input subcarriers.
10. The method of claim 8, further comprising using direct mapping in at least one DCT precoder stage, wherein said direct mapping forms the 2M output subcarriers for the given stage by taking the M input subcarriers as a length-M ordered sequence and outputting a length-2M output vector that includes the original ordered sequence interspersed with a time-reversed and mirrored version of the original ordered sequence.
11. The method of claim 9, further comprising generating the different even/odd shift control signals in consideration of the number of DCT precoder stages used for mapping each set of Ku input subcarriers.
12. The method of claim 9, further comprising generating the different even/odd shift control signals as part of a multiple-access scheduling method that uses the different patterns of even/odd shifting to differentiate between individual receivers being targeted by SC-DCT OFDM signal transmissions.
13. The method of claim 10, further comprising negating or not negating the time-reversed mirrored version of the original ordered sequence included in the length-2M output vector, in dependence on the even/odd shift control signal applied to the stage.
14. A receiver circuit configured to process a received Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal, said receiver circuit comprising:
- a signal processing chain configured to de-map N input subcarriers from the received SC-DCT OFDM signal to Ku output subcarriers, according to the formula Ku=N/2S, wherein S indicates the integer number of DCT decoder stages included in series within the signal processing chain, wherein S≥1, and wherein said signal processing chain includes a pre-processing circuit configured to remove a cyclic prefix or zero padding from N input subcarriers in advance of de-mapping;
- wherein said signal processing chain further includes one or more series DCT decoder stages following the pre-processing circuit, each such stage configured to generate M output subcarriers from 2M input subcarriers, by mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers, in dependence on a an even/odd shift control signal applied to the stage, and each such stage comprising a DCT circuit followed by an IDCT circuit; and
- wherein a first one of the DCT decoder stages takes the N input subcarriers as its 2M input subcarriers, and a last one of the DCT decoder stages provides the Ku output subcarriers as its M output subcarriers.
15. The receiver circuit of claim 14, wherein at least one DCT decoder stage in the signal processing chain comprises a direct-mapping DCT decoder stage that is configured to form the M output subcarriers by selecting a length-M ordered sequence from the 2M input subcarriers, which are known to be formed as a length-2M ordered sequence of the length-M ordered sequence interspersed with a time-reversed and mirrored version of the length-M ordered sequence.
16. The receiver circuit of claim 14, further comprising a parallel-to-serial converter circuit configured to convert the Ku output subcarriers into a corresponding serial stream, and a processing circuit configured to obtain information symbols of interest from the serial stream.
17. The receiver circuit of claim 14, wherein S>1.
18. A method for use in a receiver circuit configured to process a received Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal, said method comprising:
- removing a cyclic prefix or zero padding from N input subcarriers from the received SC-DCT OFDM signal;
- de-mapping said N input subcarriers from the received SC-DCT OFDM signal to Ku output subcarriers, after removing said cyclic prefix or zero padding, according to the formula Ku=N/2S, wherein S indicates the integer number of DCT decoder stages included in series within a signal processing chain of the receiver circuit, wherein S≥1; and
- wherein said de-mapping includes, in each of one or more series DCT decoder stages included in the receiver circuit, generating M output subcarriers from 2M input subcarriers, based on mapping even-numbered or odd-numbered ones of the 2M input subcarriers as said M output carriers, in dependence on a an even/odd shift control signal applied to the stage, and further comprising generating said M output carriers based on performing a DCT on the 2M input subcarriers, followed by performing an IDCT on the results obtained from said DCT.
19. The method of claim 18, further comprising, in at least one said DCT decoder stage in the signal processing chain, implementing a direct de-mapping, based on forming the M output subcarriers by selecting a length-M ordered sequence from the 2M input subcarriers, which are known to be formed as a length-2M ordered sequence of the length-M ordered sequence interspersed with a time-reversed and mirrored version of the length-M ordered sequence.
20. The method of claim 18, further comprising converting the Ku output subcarriers into a corresponding serial stream, and obtaining information symbols of interest from the serial stream.
21. The method of claim 18, wherein S>1.
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Type: Grant
Filed: Jan 19, 2016
Date of Patent: Aug 6, 2019
Assignee: Guangdong Oppo Mobile Telecommunications Corp., LTD. (Dongguan, Guangdong)
Inventor: Stefano Sorrentino (Solna)
Primary Examiner: Eric B. Kiss
Application Number: 15/000,917
International Classification: H04L 27/00 (20060101); H04L 27/12 (20060101); H04L 5/00 (20060101); H04L 27/26 (20060101);