Coordinated Multipoint Downlink Antenna Weight Optimization
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Solution Overview
Problem
Non-coordinated cellular communication systems fail to manage interference effectively, leading to performance limitations, especially for users near the cell edge, while zero-forcing coordinated transmission breaks down at high system loads by prioritizing minimal interference over signal strength.
Innovation Solution
The method involves determining antenna weights to maximize data rate for users while keeping total power transmitted below a limit and sum of interference generated at other users below a non-zero threshold, using channel response and interference constraint matrices to compute optimal input covariance matrices and weights for base stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If zero-forcing coordinated transmission is used to eliminate interference to other users, then interference to other users is reduced to zero, but the transmitted signal power to the desired user becomes very small at high system loads
Solution Approach 1:
The patent changes the interference constraint parameter from zero (zero-forcing) to a non-zero threshold (epsilon-forcing). This allows the transmission to generate some controlled interference while maintaining acceptable signal strength. The optimal input covariance matrix is computed with the constraint that interference power at other users remains below a non-zero threshold, balancing interference suppression with signal power preservation.
Solution Approach 2:
Instead of completely eliminating interference (zero-forcing), the patent applies partial action by allowing interference to exist at a controlled level (epsilon-forcing). This partial suppression of interference achieves a better balance between interfering with other users and maintaining sufficient signal power for the desired user, especially under high system load conditions.
2Device complexity
If transmission to one user is formed independently without considering interference to other users, then the transmission formulation is simple, but other-cell interference limits the performance especially for cell-edge users
Solution Approach 1:
The patent merges the transmission formulations for multiple users into a single coordinated optimization problem. Instead of forming transmissions independently, the system jointly optimizes the input covariance matrices for all users simultaneously, considering the interference implications. This combined approach enables the system to achieve higher data rates for cell-edge users by accounting for inter-user interference in the optimization.
Solution Approach 2:
The patent incorporates feedback mechanisms where the system uses channel state information and interference measurements to adaptively compute optimal transmission parameters. The feedback loop allows the system to learn from the actual interference caused by transmissions and adjust the covariance matrices accordingly, enabling dynamic optimization of data rate delivery while controlling interference.
3Productivity
If the system uses small to medium-sized cells with orthogonal multiple access, then spectral efficiency is improved, but other-cell interference becomes the main limiting factor for cell-edge users
Solution Approach 1:
The patent applies local quality by computing user-specific optimal input covariance matrices that are tailored to each user's channel conditions and interference environment. Instead of using a uniform transmission strategy, the system adapts the transmission parameters locally for each user based on their specific requirements and the current system state, enabling optimized performance for both cell-center and cell-edge users.
Data Source
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AI summary
A method for determining antenna weights for use in transmitting data from a plurality of base stations to a user device is disclosed. The antenna weights are determined using an input covariance matrix (S), and the input covariance matrix is determined subject to a predetermined power constraint and a predetermined, non-zero interference constraint.