Patent Application
20230327918
This application claims priority to Indian provisional patent application no. 202241020727 filed on Apr. 6, 2022, the complete disclosure of which, in their entirety, is herein incorporated by reference.
The embodiments herein generally relate to wireless communication systems and methods, and more particularly, to a system and method for improving channel estimation for MU-MIMO wireless antenna systems through dynamic port allocation.
In modern wireless communication systems, the uplink signal receptions are facilitated by channel estimation and symbol detection based on reference signals typically called DMRS (Demodulation Reference Signals) in 5GNR systems. To facilitate multi-user MIMO, the reference signals assigned for layers of each user for channel estimation, are expected to be orthogonal by design. The orthogonality of these references is achieved by allocating each layer of the users, the reference signals are orthogonal in time, frequency, and codes (CDM). This kind of allocation of reference signals (typically referred to as ports) involve performance trade-offs, especially in MU-MIMO scenarios.
Channel estimation reference signals for different users or different layers of the same user often occupy the same time-frequency resources in an OFDM-based downlink system. In an uplink system, the reference signals for different base stations or different layers of the same base station occupy the same time-frequency resources. Such reference signals, or pilots, are said to adopt a pilot-on-pilot arrangement since pilots fall on top of each other. Without appropriate signal processing in the receiver, this will lead to interference between the pilots that share a particular set of time-frequency resources.
In current channel estimation schemes especially in the MU-MIMO Scenarios, Demodulation reference signal (often called DM-RS in 5G) used for Channel estimation typically use the Orthogonal Cover Codes (OCC) based on Walsh Spreading to separate out either the users or the ports of a user. The Walsh code generation can be visualized in the form of the nested code tree structure. These reference signals apply CDM spreading across time-frequency to enable multiple users or layers to share the same time-frequency resources. The term DM-RS port is used to refer to a pilot sequence spread with a particular OCC and placed in a specific set of subcarrier indices, the maximum of which defines the maximum number of users or layers that can be loaded in MU-MIMO. During the Channel estimation process, the channel estimate is assumed to be constant across the time-frequency grid spanned by the CDM group. The spreading remains the same even when the number of users or layers in the MU-MIMO is lower than the total number of DM-RS ports that are available.
Accordingly, there is a need to mitigate and/or overcome drawbacks associated with current systems and methods for enabling improved channel estimation quality for some of the DM-RS ports in Uplink signal transmission for partially loaded DM-RS ports without compromising the channel estimation performance on the other ports.
The embodiments of the present disclosure facilitate the communications network to enable improved Channel estimation quality of partially loaded DM-RS ports in Uplink transmission, without compromising the estimation performance on the other ports which do not benefit from the improved performance.
The embodiments herein disclose a method of enabling transmission of uplink signal in a Multi-User Multiple Input Multiple-Output (MU-MIMO) system through dynamic DM-RS port allocation in a 5G New Radio network. The method comprising creating, by a priority Quality of Service (QoS) scheduler, a scheduling information and a scheduling decision for MU-MIMO Scheduling of a plurality of User equipment's (UE's), transmitting the scheduling information as Downlink Control Indicator (DCI) payload bits over a Physical Downlink Control Channel (PDCCH) to the one or more paired UEs, demultiplexing, by a demultiplexer (UEDE−MUX), one of more paired UEs of the plurality of UE's based on the scheduling information, performing a Physical Uplink Shared Channel (PUSCH) Modulation based on the scheduling information extracted from the PDCCH from the one or more paired UEs, performing Cyclic Redundancy Check (CRC) encoding and bit processing of the DCI payload bits obtained from each of the one or more UE's. The method further comprises performing, at a receiver, at least one of data modulation mapping, layer mapping, precoding and resource mapping of a processed DCI payload bit data, performing antenna resource remapping and beam combining on the PUSCH channel. The method further comprises selecting, by a resource de-mapper at the receiver, DM-RS references from a received DM-RS sequence or and the PUSCH payload for channel estimation and obtaining, by a channel estimator unit, at the receiver improved channel estimates by dynamically reducing a despreading factor in Variable Spreading Factor Orthogonal Cover Code (VSFOCC) based on a Partial port occupancy (P-Poi) at a Base-station. The channel estimates obtained are interpolated using a liner or DFT interpolator to estimate the channel over NPRB subcarriers.
According to the embodiments herein, the method further comprises, inputting the determined channel estimates to an equalizer module and performing one or more of demodulation, scrambling, Low-Density Parity-Check (LDPC) processing and CRC detachment of the inputted channel estimates.
According to the embodiments herein, the scheduling decisions comprises at least one of user pairing details, user layers, Modulation and Coding Scheme (MCS) assignment and resource assignment across time frequency grids.
According to the embodiments herein, wherein bit processing comprises at least one of Code Block segmentation, LDPC Encoding, Rate-Matching, Code-block concatenation and Scrambling at ULSCH (Uplink transport block).
According to the embodiments herein, the method further comprising performing a Hybrid automatic repeat request (HARQ) Process for each transport block by storing different Redundancy version (RV) of the data for each code-block corresponding to the ULSCH for retransmission and scheduling HARQ retransmissions based on CRC failure and data corresponding to HARQ process data maintained in a HARQ buffer.
According to the embodiments herein, the Scheduling Aware UE Port Mapper performs port assignment for reference signal (DM-RS) ports based on a Scheduling Information structure, where the Scheduling Information structure to assign the DM-RS ports comprises data layers, allocated MCS and the number of antenna ports.
According to the embodiments herein, the channel estimation is performed through at least one of least square, OCC de-spreading, frequency domain interpolation and denoising and time axis interpolation of DMRS reference signals.
According to the embodiments herein, the priority QoS scheduler creates the scheduling information based on the PHY measurements and buffer status of the uplink PDU from the higher layers.
According to the embodiments herein, the PUSCH data generated from the one or more UEs are combined through a Precoder, mapped to antennae through Antenna Mapping and subjected to orthogonal frequency-division multiplexing (OFDM) Modulation and Radio Processing at the UE. Here the PUSCH resources to be mapped to time-frequency grid is derived from the Scheduling Information.
In another aspect, the embodiments herein disclose Multi-User Multiple Input Multiple-Output (MU-MIMO) system for enabling transmission of uplink signal through dynamic DM-RS port allocation in a 5G New Radio (NR) network. The system comprising a transmitter comprising of a priority Quality of Service (QoS) scheduler to generate a scheduling information and a scheduling decision for MU-MIMO Scheduling of a plurality of User equipment's (UE's), transmit the scheduling information as Downlink Control Indicator (DCI) payload bits over a Physical Downlink Control Channel (PDCCH) to one or more paired UEs, a demultiplexer (UEDE−MUX) to demultiplex one of more paired UEs of the plurality of UE's based on the scheduling information, a Physical Uplink Shared Channel (PUSCH) Modulation unit to perform a PUSCH modulation based on the scheduling information extracted from the PDCCH from the one or more paired UEs and a Cyclic Redundancy Check (CRC) Unit to perform Cyclic Redundancy Check (CRC) encoding and bit processing of the DCI payload bits obtained from each of the one or more paired UEs. The system further comprises a receiver comprising of a Scheduling Aware UE Port Mapper Unit to perform at least one of data modulation mapping, layer mapping, precoding and resource mapping of a processed DCI payload bit data, perform antenna resource remapping and beam combining on the PUSCH channel and select DM-RS references from a received DM-RS sequence or and the PUSCH payload for channel estimation and a channel estimator unit to obtain improved channel estimates by dynamically reducing a despreading factor in Variable Spreading Factor Orthogonal Cover Code (VSFOCC) based on a Partial port occupancy (P-Poi) at a Base-station and an interpolator to interpolate the channel estimates obtained to estimate the channel over NPRB subcarriers.
According to the embodiments herein, the channel estimator unit is further configured to input the determined channel estimates to an equalizer module and perform one or more of demodulation, scrambling, Low-Density Parity-Check (LDPC) processing and CRC detachment of the inputted channel estimates.
According to the embodiments herein, the Scheduling Aware UE Port Mapper Unit is further configured to perform a Hybrid automatic repeat request (HARQ) Process for each transport block by storing different Redundancy version (RV) of the data for each code-block corresponding to the ULSCH for retransmission and schedule HARQ retransmissions based on CRC failure and data corresponding to HARQ process data maintained in a HARQ buffer. The Scheduling Aware UE Port Mapper Unit performs port assignment for reference signal (DM-RS) ports based on a Scheduling Information structure, where the Scheduling Information structure to assign the DM-RS ports comprises data layers, allocated MCS and the number of antenna ports.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein enable enhancement in the overall throughput or fairness with improved Channel Estimation on selected MU-MIMO ports in uplink transmission. Scheduling aware port allocation involves the allocation of ports to users based on the scheduling information like MCS and the number of users sharing the same time-frequency resource. Scheduling aware DM-RS port allocation ensures the allocation of users in a specific order as propose, wherein the allocation of the DM-RS ports allows the receiver to de-spread the received pilots such that some ports get the benefit with an increased number of distinct channel estimates. The base station applies the optimized Channel estimation for the UE by bypassing the frequency despreading process. The increase of the number of distinct channel estimates is possible because the FD-CDM de-spreading is no longer required for certain ports. Such a de-spreading with a lower spreading factor is allowed because the OCCs used in DM-RS can be seen as codes in the branches of an Orthogonal Variable Spreading Factor (OVSF) code tree. The increased number of distinct channel estimates improve the mean-squared error of the frequency interpolator for channels with high selectivity. This can translate to a block error rate (BLER) improvement for the associated ports. The improved channel estimate can also enable upgradation to a higher-order modulation scheme or a higher code rate, which could improve the fairness if the associated port had a lower order modulation or code rate than the others. Alternately, the improvement in BLER results in throughput improvement.
The embodiments disclosed herein may be applied to any pilot-on-pilot based OFDM communication system that employs reference signals, where the orthogonality of ports is decided by the Nested Codes. The term nested code is used herein to signify the codes for which sub-sequences of codes are orthogonal to the original code when orthogonality is examined over the length of the sub-sequence.
As mentioned, there remains a need for a system and a method to enable improved Channel estimation quality for some ports in both Uplink for partially loaded DM-RS ports without compromising the estimation performance on the other ports. Referring now to the drawings, and more particularly to
These transport blocks from each UE are subjected to CRC encoding followed by bit processing steps which involve the Code Block segmentation, LDPC Encoding, Rate-Matching, Code-block concatenation and Scrambling at ULSCH 312. HARQ Process for each transport block is managed by storing different Redundancy version (RV) of the data for each code-blocks corresponding to the transport block for retransmissions. The transmission of the data corresponding to the specific RV index is managed by the HARQ 314 Process. The Code-rate (MCS) for the LDPC and rate-matching is intimated in the Scheduling Information Structure. The Data modulation mapping is applied on the post bit processed data followed by Layer Mapping, Precoding and Resource Mapping 316. MCS is also used to select the required Modulation. The PUSCH resources to be mapped to time-frequency grid are derived from the Scheduling Information. The PUSCH data generated from all the UEs 308 are combined through the Precoder 318 and Mapped to antennae through the Antenna Mapping 320 and then subjected to Orthogonal Frequency Division Multiplexing (OFDM) 324 and Radio Processing 322 at the UE 308.
Antenna resource remapping is performed on the PUSCH Channel 326 followed by beam combining using a beam combiner 332. The weights for the beam combiner is computed using weight computation 332 from the SRS Channel estimator 338 through SRS channel estimation. Further, the resource de-mapper 334 separates out the references like DM-RS or PT-RS and the PUSCH payload. The DMRS reference 344 is used in the PUSCH DMRS Channel estimator 342 which typically has steps like determining a Least square at 346, VSFOCC despreading 348, Frequency Interpolation in a frequency domain interpolator 350 and Denoising and finally time axis interpolation at 352. The embodiments of the present disclosure increase number of finer channel estimates 354 and optimal estimates by dynamically reducing the despreading factor in the OCC stage (Variable Spreading Factor OCC) based on the Partial port occupancy known at the Base-station. These Channel Estimates 354 are further fed to Equalizer module 336 followed by Demodulation, Scrambling, LDPC Processing and CRC detachment. HARQ retransmissions are scheduled based on the CRC failures and soft data corresponding to HARQ process is maintained in the HARQ Buffer 314.
According to the embodiments herein, the port assignment for reference signal (DM-RS) is done using a Scheduling Aware UE Port Mapper 324 where the UE's, Corresponding Layers, Allocated MCS and the number of Antenna ports form the Scheduling Information structure are used for appropriately assigning the DM-RS ports. Group Casting must be done to send the P-Poi to all UEs scheduled, such that the UE getting MSE advantage will use the lower spreading factor while doing the channel estimation.
The priority Quality of Service (QoS) scheduler 404 generates a scheduling information and a scheduling decision for MU-MIMO Scheduling of a plurality of User equipment's (UE's) and transmits the scheduling information as Downlink Control Indicator (DCI) payload bits over a Physical Downlink Control Channel (PDCCH) to one or more paired UEs. The demultiplexer (UEDE−MUX) 406 demultiplexes one of more paired UEs of the plurality of UE's based on the scheduling information. The Physical Uplink Shared Channel (PUSCH) Modulation unit 408 performs a PUSCH modulation based on the scheduling information extracted from the PDCCH from the one or more paired UEs. The Cyclic Redundancy Check (CRC) Unit 410 further preforms a Cyclic Redundancy Check (CRC) encoding and bit processing of the DCI payload bits obtained from each of the one or more paired UEs.
According to the embodiments herein, the receiver 414 comprises a Schedule Aware UE Port Mapper unit 416, a channel estimator unit 418 and an interpolator 420, where the interpolator DFT or linear. The Scheduling Aware UE Port Mapper Unit 416 is configured to perform at least one of data modulation mapping, layer mapping, precoding and resource mapping of a processed DCI payload bit data, perform antenna resource remapping and beam combining on the PUSCH channel; and select DM-RS references from a received DM-RS sequence or and the PUSCH payload for channel estimation. The channel estimator unit 418 is configured to obtain improved channel estimates by dynamically reducing a despreading factor in Variable Spreading Factor Orthogonal Cover Code (VSFOCC) based on a Partial port occupancy (P-Poi) at a Base-station. Further the interpolator is configured to interpolate the channel estimates obtained to estimate the channel over NPRB subcarriers. The channel estimator unit 418 is further configured to input the determined channel estimates to an equalizer module and perform one or more of demodulation, scrambling, Low-Density Parity-Check (LDPC) processing and CRC detachment of the inputted channel estimates. The scheduling decisions comprises at least one of user pairing details, user layers, Modulation and Coding Scheme (MCS) assignment and resource assignment across time frequency grids. The bit processing comprises at least one of Code Block segmentation, LDPC Encoding, Rate-Matching, Code-block concatenation and Scrambling at ULSCH (Uplink transport block).
The Scheduling Aware UE Port Mapper Unit 416 is further configured to perform a Hybrid automatic repeat request (HARQ) Process for each transport block by storing different Redundancy version (RV) of the data for each code-block corresponding to the ULSCH for retransmission and schedule HARQ retransmissions based on CRC failure and data corresponding to HARQ process data maintained in a HARQ buffer. The Scheduling Aware UE Port Mapper Unit 416 is further configured to perform port assignment for reference signal (DM-RS) ports based on a Scheduling Information structure, where the Scheduling Information structure to assign the DM-RS ports comprises of data layers, allocated MCS and a plurality of antenna ports.
The channel estimator unit 418 performs channel estimation through at least one of least square, OCC de-spreading, frequency domain interpolation and denoising and time axis interpolation of DMRS reference signals. Here the PUSCH resources to be mapped to time-frequency grid is derived from the Scheduling Information and the PUSCH data generated from the one or more UEs are combined through a Precoder, mapped to antennae through Antenna Mapping and subjected to orthogonal frequency-division multiplexing (OFDM) Modulation and Radio Processing at the UE.
The priority QoS scheduler 402 herein creates the scheduling information based on the PHY measurements and buffer status of the uplink PDU from the higher layers.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202241020727 | Apr 2022 | IN | national |
