3D DFT Space-Frequency Multiplexing for Massive MIMO Interference
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Solution Overview
Problem
Current LTE-Advanced systems face limitations in simultaneously serving a large number of users due to the limited number of antennas, leading to inter-user interference and inefficient spectral usage, especially in massive MIMO systems where traditional beamforming and precoding techniques require significant feedback and computational resources.
Innovation Solution
A method utilizing three-dimensional Discrete Fourier Transforms (DFT) for orthogonal space-frequency multiplexing, allowing base stations with large antenna arrays to serve as many users as antennas without inter-user interference by selecting appropriate grid spacings and employing a combined space-frequency scheduler to allocate resources efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional beamforming and precoding techniques are used in LTE-Advanced systems, then spatial separation of users is achieved, but the number of simultaneously served users is limited to the number of antennas (maximum eight) and significant feedback is required
Solution Approach 1:
The patent extends traditional single-dimensional beamforming into three-dimensional space-frequency beamforming by incorporating both spatial dimensions (azimuth and elevation) and frequency domain resources. This dimensional expansion allows the system to serve more users simultaneously by creating orthogonal beams in multiple dimensions, overcoming the limitation of being constrained only by the number of antennas in traditional approaches
Solution Approach 2:
The patent segments the large antenna array into multiple sub-arrays, where each sub-array independently serves a group of users. This segmentation reduces the feedback overhead by allowing localized beamforming decisions for each sub-array while maintaining overall system coordination, thereby serving more users without proportionally increasing feedback requirements
2Measurement precision
If traditional beamforming is used to direct radiated patterns towards intended users, then spatial focusing is achieved, but beam side lobes cause inter-user interference requiring a large subset of antennas per user
Solution Approach 1:
By adding the frequency domain as an additional dimension to traditional spatial beamforming, the patent creates orthogonal frequency resources for different user groups. This frequency domain separation eliminates inter-user interference caused by spatial side lobes, as users experience isolated frequency bands even when spatial beams overlap
Solution Approach 2:
The patent applies different beamforming strategies to different spatial and frequency regions. Each sub-array focuses energy locally at its designated users with optimized beam patterns, while frequency domain division ensures that local interference from side lobes does not affect other users in different frequency bands
3Productivity
If massive MIMO systems with several hundreds of antennas are deployed, then spectral efficiency increases, but computational complexity and feedback requirements become impractical
Solution Approach 1:
The patent divides the massive antenna array into multiple manageable sub-arrays, each handling a subset of users independently. This segmentation reduces computational complexity by allowing parallel processing of smaller sub-problems rather than computing beamforming for all hundreds of antennas simultaneously, while still achieving high spectral efficiency through coordinated multi-sub-array operation
Solution Approach 2:
By utilizing frequency domain division in addition to spatial dimensions, the patent distributes the computational load across frequency resources. Each frequency band handles a subset of users with reduced computational requirements, and the overall spectral efficiency is achieved through the cumulative effect of multiple frequency bands working in parallel
Data Source
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AI summary
The method comprising a base station equipped with a large number of antennas according to a two-dimensional rectangular array and a number M of cell users, said rectangular array comprising N1 antenna elements along one axis with a regular spacing dx and N2 antenna elements along a perpendicular axis with a regular spacing dy, said users being characterized by angles (θ,ϕ) in a spherical coordinate system, where in order to achieve orthogonal multiple access the method comprises: selecting a grid spacing (Δu,Δv) in the (u, v) domain; discretizing the (u, v) domain; constructing a set of signals ST[k,l,f]; calculating time-domain excitations AT[n,m,t] for the antenna elements in the array given by coordinates (ndx,mdy) for generation of the downlink transmit signals; and obtaining the frequency contents SR[k,l,f] of the complex baseband signals received from the M users in the uplink. The system implements the method of the invention.