Optimal LLR Clipping Levels for Mixed Hard/Soft Output Detection

Abstract—Consider a communications system where the detector generates a mix of hard and soft outputs, which are then fed into a soft-input channel decoder. In such a setting, it is of interest to find the optimal soft representation for the hard detected bits, which minimizes the probability of error at the decoder output. In this contribution we prove that for repetition codes transmitted over the AWGN channel using antipodal signaling, the optimal soft representation is given by the error probability at the detector output. This provides an indication of how “LLR clipping levels” should be chosen, e.g., in the context of list based detection of multiple-input multiple-output (MIMO) signals. I. MOTIVATION Consider the following communications problem: due to constraints on the allowable computational complexity, the receiver cannot make use of the optimal soft output detector. As a consequence, reliability information is unavailable for at least some of the detected bits and t...

• Type: Conference
• Year: 2008
• Where: GLOBECOM
• Authors: Ernesto Zimmermann, David L. Milliner, John R. Barry, Gerhard Fettweis
• Keywords: Detector, Detector Output, GLOBECOM 2008, Optimal Soft Representation, Telecommunications