Downlink Pre-coding in Cloud Radio Access Networks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In Cloud Radio Access Networks (C-RAN), the limited capacity of fronthaul networks restricts data transmission between baseband units (BBUs) and remote radio heads (RRHs), necessitating efficient downlink pre-coding methods to manage increasing fronthaul load and interference while optimizing digital and analog beamforming.
Innovation Solution
The method involves determining optimal digital and analog pre-coding matrices and quantization noise allocation to maximize sum rate transmission, using techniques like column-wise iteration, weighted minimum mean square error, and interference cancellation, while managing limited fronthaul capacity through bit allocation algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of RRHs is increased to enhance network capacity, then the coverage and service capability are improved, but the fronthaul load increases excessively
Solution Approach 1:
The patent divides the downlink pre-coding process into two independent stages: digital pre-coding at the BBU and analog pre-coding at the RRH. This segmentation allows the fronthaul to only transmit precoded signals rather than raw data, significantly reducing fronthaul load while maintaining the ability to support multiple RRHs
Solution Approach 2:
The patent performs digital pre-coding at the BBU before transmitting signals to RRHs. By preliminarily processing the signals with digital pre-coding matrices, the system reduces the dimensionality and complexity of signals that need to be transmitted over the fronthaul, thereby reducing fronthaul load while preserving network capacity
2Reliability
If digital pre-coding is performed to reduce interference, then the transmission quality is improved, but the computational complexity and fronthaul requirements increase
Solution Approach 1:
The patent segments the pre-coding function into digital pre-coding (BBU) and analog pre-coding (RRH). This division reduces computational complexity at the BBU by performing only digital pre-coding, while analog pre-coding at RRHs handles the remaining interference management with simpler local computations
Solution Approach 2:
The patent implements partial pre-coding by combining digital and analog stages rather than performing complete digital pre-coding. This partial approach achieves sufficient interference reduction for transmission quality while avoiding the excessive computational complexity of full digital pre-coding systems
3Ease of manufacture
If the fronthaul capacity is limited to reduce deployment cost, then the network cost is reduced, but the data transmission capability between BBU and RRHs is restricted
Solution Approach 1:
The patent changes the parameter representation of transmitted signals by applying digital pre-coding matrices that transform high-dimensional data into lower-dimensional precoded signals. This parameter transformation enables efficient transmission over limited-capacity fronthaul while maintaining data transmission capability
Solution Approach 2:
By segmenting the pre-coding function and transmitting only precoded signals over the fronthaul, the patent reduces the amount of data that needs to be transmitted. This enables deployment with limited fronthaul capacity while preserving essential data transmission capabilities between BBU and RRHs
Data Source
AI summary
A method and a system for downlink pre-coding in cloud radio access networks uses a baseband unit, a number of remote radio heads, and a number of user equipments. The baseband unit determines a received signal expression for each user equipment based on system parameters and channel state information, and determines a sum rate expression which may be achievable for downlink transmission based on the received signal expression. The baseband unit then sets up a constrained optimal problem expression subject to a maximum transmitting power of each remote radio head with an objective function of sum rate maximization based on the achievable sum rate expression, and finally determines optimal solutions for the constrained optimal problem where the optimal solutions comprise downlink pre-coding used for downlink transmission.