Distributed Base Station Fronthaul Precoding Segmentation
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Solution Overview
Problem
The existing distributed base station systems face challenges in efficiently managing fronthaul link capacity, especially with massive MIMO configurations, where the overhead of precoding coefficients dominates the fronthaul link traffic, and current split options either increase costs or limit coordination and scalability.
Innovation Solution
Decomposing precoding into two parts, with the BBU performing interference mitigation and the RRU concentrating energy, allowing for efficient use of fronthaul capacity and enabling full MIMO gain while allowing user-layer signal coordination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all precoding coefficients are calculated and transmitted from BBU to RRU, then full MIMO coordination and interference mitigation are achieved, but fronthaul link overhead increases dramatically
Solution Approach 1:
The precoding function is segmented into two parts: interference mitigation precoding (IMP) performed at BBU and beamforming precoding (BF) performed at RRU. This segmentation allows the system to achieve full MIMO coordination through IMP while reducing fronthaul overhead by performing BF locally at RRU based on uplink channel estimates
Solution Approach 2:
The BBU performs interference mitigation precoding in advance on the downlink data signals before transmitting them to RRU. The RRU then applies beamforming precoding locally using preliminary channel estimates from uplink signals, eliminating the need to transmit all precoding coefficients over fronthaul
2Productivity
If IFFT and CP addition are performed in RRU (split option 7-1), then fronthaul efficiency increases, but one bit stream per antenna still requires very high fronthaul capacity for massive MIMO
Solution Approach 1:
The patent segments the signal processing function by performing IFFT and CP addition at BBU rather than RRU. This changes the split option from 7-1 to effectively option 7-3, where only processed user-layer signals need to be transmitted over fronthaul, reducing the data volume significantly while maintaining processing efficiency
Solution Approach 2:
BBU performs preliminary signal processing including IFFT and CP addition before transmitting signals to RRU. This preliminary action reduces the complexity and data rate requirements at RRU, allowing efficient massive MIMO operation with reduced fronthaul capacity requirements
3Device complexity
If BBU performs all baseband processing including precoding, then coordination between multiple RRUs is simplified, but RRU functionality is limited and system flexibility is reduced
Solution Approach 1:
The patent segments baseband processing functions between BBU and RRU: BBU performs interference mitigation precoding and IFFT, while RRU performs beamforming precoding and signal transmission. This segmentation maintains coordination simplicity at BBU while enhancing RRU functionality and flexibility
Solution Approach 2:
BBU performs preliminary interference mitigation processing before sending signals to RRU, but leaves final beamforming and transmission decisions to RRU. This preliminary action approach maintains coordination simplicity while enabling RRU to adapt to local channel conditions and perform advanced functions
Data Source
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AI summary
ABSTRACT A method is disclosed performed by an RRU (120) of a distributed base station system (100) of a wireless communication network, the distributed base station system (100) further comprises a BBU (110) connected to the RRU, the RRU (120) being connected to a plurality of antennas (121, 122, 123) through which the RRU transmits user-layer signals to a plurality of UEs (161, 162, 163). The method comprises sending information related to received uplink signals to the BBU so that the BBU can obtain a first part of precoding coefficients to be used for precoding digital user-layer signals. The method further comprises obtaining a second part of the precoding coefficients and receiving, from the BBU, the digital user-layer signals precoded using the first part of the precoding coefficients. The method further comprises precoding the received digital user- layer signals precoded with the first part of the precoding coefficients also with the second part of the precoding coefficients, and transmitting the user-layer signals to the plurality of UEs (161, 162, 163) via the plurality of antennas (121, 122, 123). (Fig. 2) P73684