Interference Cancellation in TDD Massive MIMO Systems
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Solution Overview
Problem
Massive MIMO wireless communication networks face significant downlink signal interference due to pilot contamination, which limits data transmission rates despite increasing the number of antenna elements, as directed inter-cell interference persists even with infinite antennas.
Innovation Solution
The method involves estimating slow fading coefficients using received slow fading pilot signals, transmitting these coefficients to all base stations, forming aggregate sets, and using beamforming vectors to align fast fading coefficients, allowing for interference cancellation algorithms to encode robust signals for downlink transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of antenna elements is increased to improve downlink transmission capacity, then the data transmission rate is improved, but directed inter-cell interference persists due to pilot contamination
Solution Approach 1:
The base station performs preliminary estimation of slow fading coefficients using received slow fading pilot signals before downlink transmission. These coefficients are then shared with all base stations in the network, enabling proactive interference management through aggregate set formation and interference cancellation algorithms that account for pilot contamination effects
Solution Approach 2:
The system implements feedback mechanisms where base stations transmit estimated slow fading coefficients to all other base stations via backhaul links. This feedback enables network-wide coordination for interference cancellation, allowing each base station to incorporate information about interference from other cells into its downlink signal design
2Productivity
If pilot signals are reused across multiple cells to improve network capacity, then spectral efficiency is improved, but pilot contamination occurs causing interference
Solution Approach 1:
The invention converts the harmful effect of pilot contamination into a beneficial opportunity by having base stations share their estimated slow fading coefficients with all other base stations. This sharing enables the formation of aggregate sets that explicitly account for interference from pilot-reusing cells, transforming the contamination problem into structured interference that can be cancelled through coordinated signal design
Solution Approach 2:
The system changes the approach from treating pilot contamination as an unwanted side effect to utilizing it as structured information. By estimating and sharing slow fading coefficients, the system transforms the random interference into a predictable parameter that can be compensated for through aggregate set formation and interference cancellation algorithms
Data Source
AI summary
Directed inter-cell interference experienced by the downlink of a massive MIMO wireless communication network base station due to pilot contamination that occurs as a result of pilot signal reuse is significantly reduced by encoding signals to be transmitted over the downlink into robust signals. The robust signals along with corresponding beamforming vectors are transmitted over the downlink where the beamforming vectors are estimated by the base station using received fast fading pilot sequences. The encoding is performed by an interference cancellation algorithm whose use is proper when the communication network can be characterized as having one transmitter at each of its nodes (i.e., the base stations) and all the channel coefficients of the network are known by every node.