MIMO Null Beamforming for Unlicensed Band Interference
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Solution Overview
Problem
Current technologies face challenges in ensuring fair coexistence and reducing interference between LTE-U/LAA/MuLTEFire and WiFi devices in unlicensed bands, particularly due to differences in channel sensing and frame alignment, leading to potential starvation and interference issues.
Innovation Solution
A multiple input multiple output (MIMO) network node uses precoding operations to form null signal beams on estimated channels, allowing for reduced interference by transmitting signals only on orthogonal beams, thereby enhancing spectrum sharing and coexistence between different technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If LTE-U/LAA/MuLTEFire uses listen-before-talk to mitigate interference, then interference between signals is reduced, but individual devices may be starved of access when the number of devices is high
Solution Approach 1:
The patent introduces spatial dimension through MIMO beamforming to resolve the conflict between interference reduction and access availability. By forming directional null beams in the spatial domain, the system can simultaneously protect multiple devices from interference while maintaining their access rights, transforming a one-dimensional time-based LBT approach into a multi-dimensional spatial-temporal approach.
Solution Approach 2:
The system performs preliminary channel estimation and null beam formation before the listen-before-talk procedure. By pre-configuring directional nulls toward other transmitters based on estimated channel states, the system prepares the interference mitigation structure in advance, allowing devices to access the channel more efficiently without waiting for random backoff periods.
2Ease of operation
If LTE-U/LAA/MuLTEFire aligns transmissions with fixed frame boundaries, then scheduling is simplified, but WiFi transmissions occur at random times causing overlap and interference
Solution Approach 1:
The patent applies local quality by creating direction-specific null beams rather than uniform omnidirectional transmission. Each null beam is locally tailored to counteract interference from specific WiFi transmitters in particular directions, allowing LTE transmissions to maintain fixed frame boundaries while locally suppressing interference in the spatial directions where WiFi devices operate.
Solution Approach 2:
The null beam acts as an intermediary between the fixed-frame LTE transmission system and the random-access WiFi system. By inserting directional nulls in the transmission path toward WiFi devices, the system mediates the coexistence of these two different access methodologies, allowing both to operate simultaneously with reduced mutual interference.
3Productivity
If multiple LTE-U/LAA/MuLTEFire operators share the same unlicensed band, then spectrum utilization is improved, but interference between operators increases
Solution Approach 1:
The patent segments the spatial spectrum into multiple directional beams, each with its own null structure. By dividing the omnidirectional transmission space into angular segments and creating operator-specific nulls in each segment, multiple operators can simultaneously utilize the same frequency band without excessive mutual interference, as each operator's transmission is spatially segmented away from others.
Solution Approach 2:
The system dynamically changes transmission parameters including beamforming weights and null directions based on the spatial distribution and channel characteristics of other operators. By adapting these parameters in real-time according to detected interferers, the system optimizes spectrum sharing among multiple operators, allowing higher utilization while maintaining acceptable interference levels through continuous parameter adjustment.
Data Source
AI summary
A multiple input multiple output network node, an access network node, a computer program and method are disclosed. The method comprises prior to transmitting signals in an unlicensed band: estimating at least one channel within the unlicensed band between at least one access network node operable to transmit in the unlicensed band and the multiple input multiple output network node; determining precoding operations required to generate a null signal beam for the at least one estimated channel; monitoring the unlicensed band using the determined precoding operations. In response to detecting the unlicensed band to be clear of signals: transmitting at least one signal in the unlicensed band with the null beam in place such that no signal is transmitted on the at least one estimated channel.