MIMO-OFDM Eigenbeamforming Feedback Reduction
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Solution Overview
Problem
In MIMO-OFDM systems, the existing eigenbeam forming method requires significant feedback information, especially when the number of transmit antennas is large or the mobile station's speed is high, due to the need for instantaneous channel feedback, which increases the burden on the system and hinders efficient beam forming.
Innovation Solution
The proposed solution reduces feedback information by using a method where the spatial covariance matrix is calculated for one subcarrier and applied to all subcarriers, allowing for long-term feedback of eigenbeam forming vectors and short-term feedback of the best eigenmode, thereby reducing the amount of feedback required and maintaining orthogonality of eigenbeam vectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If eigenbeam forming method is applied to OFDM system with multiple transmit antennas, then signal-to-noise ratio gain and selection diversity gain are obtained, but amount of feedback information becomes very large
Solution Approach 1:
The patent segments the feedback information into two parts: long-term spatial covariance matrix (updated slowly) and short-term channel state information (updated quickly). This segmentation allows the system to maintain accurate beamforming while reducing feedback overhead, as the spatial covariance matrix does not need to be fed back frequently.
Solution Approach 2:
The patent performs preliminary calculation of the spatial covariance matrix at the mobile station based on uplink channel measurements. By pre-calculating this matrix and only feeding back essential information (eigenvectors and eigenvalues), the system reduces the amount of feedback required while maintaining beamforming performance.
2Measurement precision
If instantaneous channel information is fed back for each subcarrier, then accurate beam forming is achieved, but feedback burden becomes severe
Solution Approach 1:
The patent calculates a single spatial covariance matrix that serves all subcarriers in the OFDM system. This universal matrix captures the spatial characteristics of the MIMO channel and can be reused across multiple subcarriers, eliminating the need to feed back separate beamforming vectors for each subcarrier.
Solution Approach 2:
The patent changes the feedback parameter from subcarrier-specific beamforming vectors to a spatial covariance matrix that represents the overall spatial characteristics. This parameter change reduces feedback overhead while maintaining the ability to perform accurate beamforming across all subcarriers.
3Strength
If number of transmit antennas is increased, then antenna array gain is improved, but feedback rate for tracking channel variation increases
Solution Approach 1:
The patent implements a dynamic feedback mechanism where the spatial covariance matrix is updated at a slower rate than the channel state information. This dynamic approach allows the system to adapt to channel variations while reducing feedback rate, as the spatial covariance matrix changes more slowly than the instantaneous channel state.
Data Source
AI summary
Disclosed is a MIMO-OFDM system, wherein the transmitter comprises a serial/parallel converter for converting continuously inputted symbols of the number of subcarriers to K parallel signals; a signal reproducer for reproducing K parallel signals by the number of transmit antennas L an eigenmode generator for generating eigenbeam of the reproduced signals outputted from the signal reproducer at each subcarrier, on the basis of Nf eigenbeam forming vectors which are fed back long-term and information of a best eigenbeam forming vector at each subcarrier which is fed back short-term, through the feedback device; and a plurality of inverse Fourier converters for receiving the signals outputted from the eigenmode generator and generating an OFDM symbol.