Reduced Complexity Space-Time Code for MIMO Receiver
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Solution Overview
Problem
The complexity of existing space-time codes in MIMO systems, particularly with 16-QAM and 64-QAM signal constellations, leads to prohibitively high computational requirements for optimum receivers, necessitating suboptimum receivers that degrade performance.
Innovation Solution
A method for transmitting and estimating symbols using a reduced complexity 2×2 space-time code, where each component of the coding matrix is a linear combination of two symbols, and the receiver computes intermediate signals to estimate symbols with minimal Euclidean distance calculations, reducing complexity to the square of the signal constellation size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional space-time codes with 16-QAM or 64-QAM signal constellations are used, then the signal transmission capacity and diversity are improved, but the receiver complexity increases prohibitively (M^4 Euclidean distance computations)
Solution Approach 1:
The patent segments the symbol estimation process into two independent stages: first estimating (s1, s2) by computing M^2 Euclidean distances, then estimating (s3, s4) using the same approach. This segmentation reduces the overall complexity from M^4 to M^2 computations while maintaining full-diversity space-time coding with a 2×2 coding matrix
Solution Approach 2:
The patent introduces an intermediate estimation step where the receiver first computes estimates of (s1, s2) as intermediary results, then uses these intermediates to compute final estimates of (s3, s4). This intermediary approach enables the system to achieve optimal performance with reduced computational burden
2Device complexity
If suboptimum receivers are used to reduce complexity, then the receiver complexity is reduced, but the performance degradation occurs
Solution Approach 1:
The patent changes the parameter structure of the space-time code by using a specific 2×2 coding matrix formulation where each element is a linear combination of two symbols. This parameter change enables the receiver to achieve optimal performance with M^2 complexity instead of M^4, eliminating the need for suboptimum receivers
3Productivity
If full-rate full-diversity 2×2 space-time coding is implemented with conventional approaches, then the transmission rate and diversity order are improved, but the computational burden becomes prohibitive (M^4 Euclidean distance computations)
Solution Approach 1:
The patent segments the estimation of four symbols into two independent estimation processes, each handling two symbols. This segmentation maintains the full-rate transmission capability while reducing the computational burden from M^4 to M^2 Euclidean distance computations
Solution Approach 2:
The patent transforms the four-dimensional symbol estimation problem into two separate two-dimensional estimation problems by exploiting the structure of the 2×2 coding matrix. This dimensional transformation maintains transmission efficiency while dramatically reducing computational requirements
Data Source
AI summary
An embodiment of a method for transmitting a sequence of symbols through at least a channel in a wireless communication system includes: forming a coding matrix with the sequence of symbols, each component of the coding matrix being a linear combination of two symbols among a first, a second, a third, and a fourth symbol (s1, s2, s3 , s4), transmitting a first component and a second component of a first column and of a second column of the coding matrix through a first transmit antenna and a second transmit antenna at a first and a second time slot wherein the coding matrix is defined as(as1+bs3-cs2*-ds4*as2+bs4cs1*+ds3*),a, b, c, d being complex numbers of modulus 1.