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US-12627529-B2 - Systems and methods for enhancing efficient uplink MIMO performance and implementation for O-RAN-based radio access networks

US12627529B2US 12627529 B2US12627529 B2US 12627529B2US-12627529-B2

Abstract

A system and method of operating an Open Radio Access Network (O-RAN, in which O-RAN the system includes: a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); an O-RAN radio unit (O-RU) remote from the BBU; and a fronthaul interface between the O-RU and the BBU. A functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL) so that at least one of i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

Inventors

  • Javad Abdoli
  • Ali Fatih Demir
  • Wessam Afifi Ahmed
  • Young-Han Nam

Assignees

  • MAVENIR SYSTEMS, INC.

Dates

Publication Date
20260512
Application Date
20220916

Claims (13)

  1. 1 . An Open Radio Access Network (O-RAN) system, comprising: a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); an O-RAN radio unit (O-RU) remote from the BBU; and a fronthaul interface between the O-RU and the BBU; wherein a functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL), and wherein the system is configured such that i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, and ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL.
  2. 2 . The system according to claim 1 , wherein the system is configured such that the O-DU transfers DM-RS information to the O-RU, the DM-RS information including DM-RS configuration parameters of the scheduled or paired UEs/layers are received by the O-RU, and the O-RU generates a DM-RS sequence using the DM-RS configuration parameters received from O-DU.
  3. 3 . The system according to claim 2 , wherein the system is configured such that the O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at a current slot n using the DM-RS information.
  4. 4 . The system according to claim 3 , wherein the system is configured such that the O-RU equalizes the UL channels of the one or more UEs, the one or more layers, or both transmitted at a current slot n.
  5. 5 . The system according to claim 4 , wherein the system is configured such that the O-RU calculates a supplementary demodulation information and transfers the supplementary demodulation information along with an equalized signal stream to the O-DU.
  6. 6 . The system according to claim 5 , wherein the system is configured such that the O-DU performs a demodulation on a signal of slot n transferred from the O-RU and a L1/L2 processing on the demodulated signal.
  7. 7 . The system according to claim 1 , wherein the system is configured such that iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.
  8. 8 . The system according to claim 7 , wherein the system is configured such that the O-DU transfer DM-RS information to the O-RU, the DM-RS information including DM-RS configuration parameters of the scheduled or paired UEs/layers are received by the O-RU, and the O-RU generates a DM-RS sequence using the DM-RS configuration parameters received from O-DU.
  9. 9 . The system according to claim 8 , wherein the system is configured such that the O-RU estimates the UL channels of the UE(s) and/or layer(s) transmitted at a current slot n using the DM-RS information.
  10. 10 . The system according to claim 9 , wherein the system is configured such that the O-RU equalizes the UL channels of the one or more UEs, the one or more layers, or both, transmitted at a current slot n.
  11. 11 . The system according to claim 10 , wherein the system is configured such that, prior to a slot n, the DU transfers modulation information to the RU and the O-RU performs demodulation on an equalized signal.
  12. 12 . A method of operating an Open Radio Access Network (O-RAN) system, comprising: providing a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); providing an O-RAN radio unit (O-RU) remote from the BBU; and providing a fronthaul interface between the O-RU and the BBU; wherein a functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL), and wherein i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, and ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL.
  13. 13 . The method according to claim 12 , wherein iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.

Description

CROSS REFERENCE TO RELATED APPLICATIONS The present application claims priority to U.S. Provisional Patent Application No. 63/244,774, filed on Sep. 16, 2021, U.S. Provisional Patent Application No. 63/257,811, filed on Oct. 20, 2021, and U.S. Provisional Patent Application No. 63/300,108, filed on Jan. 17, 2022, the entirety of each of which is incorporated herein by reference. BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure The present disclosure relates to systems and methods for operating the Radio Access Network (RAN) design for 4G- and 5G-based mobile networks, and relates more particularly to systems and methods to enable efficient uplink mMIMO performance for Open-RAN (O-RAN). Traditionally, the radio access networks were built as an integrated unit where the entire RAN was processed. The RAN network traditionally uses application-specific hardware for processing, making them difficult to upgrade and evolve. As future networks evolve to have massive densification of networks to support increased capacity requirements, there is a growing need to reduce the CAPEX/OPEX costs of RAN deployment and make the solution scalable and easy to upgrade. In the field of cloud-based Radio Access Networks (RAN), a significant portion of the RAN layer processing is performed at a central unit (CU) and a distributed unit (DU). Both CUs and DUs are also known as the baseband units (BBUs). CUs are usually located in the cloud on commercial off-the-shelf servers, while DUs can be distributed. Also, the RF and real-time functions can be processed in the remote radio unit (RU). The context of the present disclosure is related to systems and methods to enable efficient uplink mMIMO performance for O-RAN-based RANs. 3GPP has defined multiple split options across the entire radio access network (RAN). There are various factors affecting the selection of the fronthaul split option, such as bandwidth, latency, implementation cost, virtualization benefits, complexity of the fronthaul interface, expansion flexibility, computing power, and memory requirement. One of the most common splits that are standardized recently by the O-RAN alliance is split option 7-2x (Intra-PHY split). This split has multiple advantages such as simplicity, transport bandwidth scalability, beamforming support, interoperability, support for advanced receivers and inter-cell coordination, lower O-RU complexity, future proof-ness, and interface and functions symmetry. One of the technologies that use the O-RAN 7-2x specifications is 4G/5G massive MIMO (mMIMO). In SU-MIMO, the gNB serves a single user on a set of time-frequency resources, whereas in MU-MIMO setup, the gNB serves multiple users on the same time-frequency resources. In UL, UEs send SRS signals over a relatively long period of time, which are sent to the O-DU from the O-RU via the fronthaul interface. Using the SRS signal, the O-DU then obtains the UL channel estimates of the UEs, using which gNB performs user pairing (in the case of MU-MIMO) and calculates UL combining/digital beamforming matrix for the scheduled user(s). The O-DU sends the combining/digital beamforming matrix elements or weights to the O-RU, which in return applies these elements to the frequency-domain PUSCH IQ samples received at a later time and sends the resulting IQ samples to the O-DU for the rest of PHY processing. One aspect of the combining operation (using the combining/digital beamforming matrix) at O-RU is that it enables the O-RU to reduce the number of streams transferred from O-RU to O-DU to a value smaller than the number of RX antennas. In mMIMO systems, the number of RX antennas is large, and transferring all received streams for PUSCH to O-DU incurs significant and prohibitive front-haul bandwidth consumption. Although split option 7-2x enables multiple advanced features, such as beamforming and UL CoMP, the system performance may degrade in certain scenarios, such as UL mMIMO for high-speed UEs and/or interference-limited scenarios, where there is significant inter-cell interference (ICI) from neighboring cells contaminating the UL signal from the desired UEs. Performance degradation in high mobility scenarios: The reason for such degradation in high-speed UEs scenarios is channel aging. Specifically, the SRS signals are sent over a relatively long period of time (e.g., 10s of milliseconds). By the time the O-RU applies the combining/digital beamforming matrix elements to the PUSCH symbols, these matrix elements become inaccurate since the SRS signals are outdated (i.e., SRS to UL-data TTI delay is long). In other words, the channel gains between the UEs and the gNB at the time PUSCH is received are no longer reflected accurately by the SRS signals (since UEs are moving fast in such a scenario), which cause interference and hence throughput degradation during the combining process (using the combining/digital beamforming matrix) in the UL chain. Performance degradation in the presence of inter-cel