Distributed Base Station Uplink Signal Processing via Decomposed Zero-Forcing
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Solution Overview
Problem
Current distributed base station systems face challenges in balancing the complexity of remote radio units (RRUs) with the capacity limitations of fronthaul links, particularly in handling inter-cell interference in uplink MIMO systems, which limits scalability and increases costs.
Innovation Solution
A method is introduced where the RRU performs simpler processing like maximum ratio combining, and the BBU handles more complex operations like interference rejection, using a decomposed Zero-Forcing (ZF) method to reduce fronthaul traffic while mitigating both intra-cell and inter-cell interferences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RRU performs full MIMO processing including interference rejection, then interference mitigation performance is improved, but device complexity increases significantly
Solution Approach 1:
The patent segments the MIMO processing into two parts: maximum ratio combining (MRC) performed at the RRU and interference rejection combining (IRC) performed at the BBU. This segmentation allows the RRU to perform only simple MRC operations, reducing its complexity while the BBU handles the more complex IRC processing for interference mitigation.
Solution Approach 2:
The patent introduces an intermediary processing step where the RRU performs MRC and sends processed signals to the BBU, which then performs IRC. This intermediary approach allows the system to achieve full interference rejection performance without requiring the RRU to have full IRC capability, thus reducing RRU complexity.
2Productivity
If the number of antennas at the RRU is increased, then spectrum efficiency is improved, but the required fronthaul link capacity increases proportionally
Solution Approach 1:
The patent segments the signal processing to perform MRC at the RRU before transmitting to the BBU. This segmentation reduces the amount of data that needs to be transmitted over the fronthaul link compared to transmitting raw antenna signals, thereby reducing the required fronthaul capacity while maintaining the ability to support multiple antennas for spectrum efficiency.
Solution Approach 2:
The patent performs preliminary MRC processing at the RRU before transmitting signals to the BBU. This preliminary action combines signals from multiple antennas into fewer streams, reducing the fronthaul capacity requirements while preserving the spectral efficiency benefits of having multiple antennas.
3Quantity of substance
If all MIMO processing is moved to the RRU to reduce fronthaul traffic, then fronthaul capacity is reduced, but device complexity at the RRU increases significantly
Solution Approach 1:
The patent segments the MIMO processing functions between RRU and BBU, with the RRU performing only MRC and the BBU performing IRC. This segmentation achieves fronthaul traffic reduction without requiring the RRU to handle the full complexity of MIMO processing, as the complex IRC is offloaded to the BBU.
Solution Approach 2:
The patent applies partial MIMO processing at the RRU (only MRC) rather than complete MIMO processing. This partial action is sufficient to reduce fronthaul traffic significantly while the remaining processing (IRC) is handled by the BBU, avoiding excessive RRU complexity.
4Device complexity
If the RRU performs maximum ratio combining only, then device complexity is reduced, but interference rejection capability is weakened
Solution Approach 1:
The patent uses the BBU as an intermediary to perform IRC processing on signals that have been pre-processed by MRC at the RRU. This intermediary approach allows the RRU to remain simple while the system as a whole maintains full interference rejection capability through the BBU's IRC processing.
Solution Approach 2:
The patent performs preliminary MRC at the RRU to prepare signals for subsequent IRC processing at the BBU. This preliminary action simplifies the RRU's task while ensuring that the signals are properly conditioned for the interference rejection that will be performed centrally at the BBU.
Data Source
AI summary
Disclosed is a method performed by a RRU of a distributed base station system of a wireless communication network, the RRU being connected to a BBU over a fronthaul link, the RRU being connected to N antennas. The method comprises obtaining uplink signals as received at the antennas from UEs wirelessly connected to the RRU, and obtaining a channel estimation matrix of wireless communication channels between UEs and the antennas. The method further comprises determining an error estimation matrix based on the channel estimation matrix, and on received reference signals yref,l, the received reference signals having L symbols, L being smaller than N, determining intermediate signals, based on the uplink signals, the channel estimation matrix and the error estimation matrix, and sending to the BBU over the fronthaul link, the determined intermediate signals.