LTE Random Access Beamforming for Interference Reduction
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Solution Overview
Problem
In wireless communication systems, especially in LTE, the random access procedure faces challenges with strong inter-cell interference, leading to decoding failures and increased random access delay due to broadcasted random access responses (RARs) being received by UEs, which results in collisions with other broadcast messages and unavailable PDCCH resources.
Innovation Solution
Implementing horizontal/vertical beamforming techniques by mapping the preamble to specific beams using an enhanced RA-RNTI, allowing the eNB to transmit RARs using UE-specific search spaces, thereby reducing collisions and improving SINR, and using 2D antenna arrays for sectorization to direct beams more accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If beamforming is used to direct narrow beams at mobile units, then system capacity and signal-to-interference ratio are improved, but device complexity increases due to smart antenna arrays
Solution Approach 1:
The patent segments the coverage area into multiple sectors using 2D antenna arrays, with each sector served by dedicated beamforming weights. This segmentation allows the system to achieve high capacity through focused beams while managing complexity by dividing the overall antenna array into manageable sector-specific sub-arrays.
Solution Approach 2:
The patent applies local quality by using UE-specific search spaces and beam-specific RAR transmissions tailored to individual user equipment and beam directions. Each UE receives customized RAR messages through dedicated beams rather than broadcast to all UEs, improving signal quality and reducing interference while maintaining system capacity.
2Reliability
If RARs are broadcasted to all UEs, then random access response is provided, but collisions with other broadcast messages occur and PDCCH resources become unavailable
Solution Approach 1:
The patent extracts RAR transmissions from the common broadcast channel and places them in UE-specific search spaces. This extraction removes RAR messages from the crowded broadcast channel, eliminating collisions with other broadcast messages and freeing up PDCCH resources for other purposes.
Solution Approach 2:
The patent introduces beam-specific indicators and UE-specific search spaces as intermediaries between the RAR transmission and the UEs. These intermediaries enable targeted delivery of RAR messages through specific beams rather than broad broadcasting, reducing delays and improving reliability.
3Area of stationary object
If conventional antennas radiate energy to all mobile units, then coverage area is maintained, but interference between mobile units increases
Solution Approach 1:
The patent changes the spatial distribution parameters of transmitted energy by using smart antenna arrays to form directed beams instead of omnidirectional radiation. This parameter change concentrates energy in specific directions, maintaining coverage area while significantly reducing interference between mobile units through spatial separation.
Solution Approach 2:
The patent introduces spatial dimensionality through 2D antenna arrays and beamforming, transitioning from planar coverage to three-dimensional beam steering. This dimensional change allows the system to maintain coverage area while reducing interference by directing beams in specific spatial directions rather than radiating uniformly in all directions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the random access procedure by reducing collisions, improving received SINR, and decreasing random access delay through targeted beamforming, ensuring reliable RAR transmission and increased system capacity.
Implementation Method 1
The eNB may determine a selected horizontal/vertical beam for the UE based on the received preamble. The eNB may then transmit a random access response (RAR) to the UE using the selected horizontal/vertical beam.
Implementation Method 2
Smart antennas are arrays of antenna elements, each of which receive a signal to be transmitted with a predetermined phase offset and relative gain. The net effect of the array is to direct a (transmit or receive) beam in a predetermined direction. The beam is steered by controlling the phase and gain relationships of the signals that excite the elements of the array.
Data Source
AI summary
A method for improved random access procedures by a UE is provided. The method comprises: measuring a common CSI-RS; selecting a best horizontal/vertical beam from a set of fixed beams; determining a preamble mapped to the selected horizontal/vertical beam; transmitting the preamble; and receiving a random access response.