MIMO Receiver LLR Generation via Modified Maximum Likelihood Decoding
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Solution Overview
Problem
Current Spatial Multiplexing (SM) communication systems face challenges in generating high-reliability Log Likelihood Ratios (LLRs) with low computational complexity, particularly due to the exponential increase in complexity of existing methods like the Maximum Likelihood (ML) scheme and error propagation in schemes like Successive Interference Cancellation (SIC).
Innovation Solution
A receiver apparatus and method that performs Modified Maximum Likelihood (MML) decoding in ascending or descending order of transmit antennas to estimate candidate vectors, calculates Euclidean distances, and computes LLRs using these distances, effectively reducing complexity while approaching the performance of ML receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Maximum Likelihood (ML) scheme is used to calculate Euclidean distances for all symbols within a constellation, then reliability of LLR generation is improved, but computational complexity increases exponentially
Solution Approach 1:
The patent segments the ML decoding process by fixing the symbol from one transmit antenna and independently determining symbols from other transmit antennas. This divides the exhaustive M^NT search into M separate sub-problems, each requiring only M^(N-1) operations, thereby reducing complexity from exponential to linear in the number of transmit antennas while maintaining ML reliability
Solution Approach 2:
The patent performs partial ML decoding by fixing one symbol and only searching for remaining symbols rather than exhaustively searching all symbol combinations. This partial action approach achieves sufficient reliability for LLR generation without the full computational burden of complete ML decoding
2Device complexity
If Successive Interference Cancellation (SIC) scheme is used to remove interference, then computational complexity is reduced, but error propagation occurs and reliability deteriorates
Solution Approach 1:
The patent performs preliminary determination of candidate symbols from each transmit antenna before combining them to form candidate transmit vectors. This preliminary action allows the system to identify reliable candidate symbols independently, avoiding the error propagation that occurs in SIC when early decisions are incorrect
Solution Approach 2:
The patent introduces an intermediary step of determining candidate symbols separately for each transmit antenna using the fixed-symbol approach, then combining these candidates to form transmit vectors. This intermediary process acts as a mediator that prevents error propagation by allowing re-evaluation of each symbol's contribution to the overall likelihood
Data Source
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AI summary
An apparatus and method for generating LLRs in an MIMO communication system. In a receiver for a spatial multiplexing communication system, a determiner performs an MML decoding operation in an ascending or descending order of TX antennas to estimate a plurality of candidate TX vectors. A distance calculator calculates a Euclidean distance for each of the candidate TX vectors from the determiner. An LLR calculator calculates LLRs using the Euclidean distances from the distance calculator. Accordingly, it is possible to generate an LLR with high reliability at low complexity in an MIMO communication system.