Efficient soft-input soft-output tree detection via an improved path metric

Jun Won Choi, Byonghyo Shim, Andrew C. Singer

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


Tree detection techniques are often used to reduce the complexity of a posteriori probability (APP) detection in multiantenna wireless communication systems. In this paper, we introduce an efficient soft-input soft-output tree detection algorithm that employs a new type of look-ahead path metric in the process of branch pruning (or sorting). While conventional path metrics depend only on symbols on a visited path, the new path metric accounts for unvisited parts of the tree in advance through an unconstrained linear estimator and adds a bias term that reflects the contribution of as-yet undecided symbols. By applying the linear estimate-based look-ahead path metric to an M-algorithm that selects the best M paths for each level of the tree, we develop a new soft-input soft-output tree detector, called an improved soft-input soft-output M-algorithm (ISS-MA). Based on an analysis of the probability of correct path loss, we show that the improved path metric offers substantial performance gain over the conventional path metric. We also demonstrate through simulations that the proposed ISS-MA can be a promising candidate for soft-input soft-output detection in high-dimensional systems.

Original languageEnglish
Article number6157084
Pages (from-to)1518-1533
Number of pages16
JournalIEEE Transactions on Information Theory
Issue number3
Publication statusPublished - 2012 Mar

Bibliographical note

Funding Information:
Manuscript received April 15, 2010; revised August 04, 2011; accepted September 22, 2011. Date of current version February 29, 2012. The work of B. Shim was supported by the Basic Science Research Program through the NRF funded by the Ministry of Education, Science and Technology (MEST) (No. 2011-0012525) and the second Brain Korea 21 project. J. W. Choi is with Qualcomm, Inc., San Diego, CA 92121 USA (e-mail: jun-wonc@qualcomm.com). B. Shim is with the School of Information and Communication, Korea University, Seoul, Korea (e-mail: bshim@korea.ac.kr). A. C. Singer is with the Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 USA (e-mail:ac-singer@illinois.edu). Communicated by F. R. Kschischang, Associate Editor for the Special Issue on “Facets of Coding Theory: From Algorithms to Networks.” Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIT.2011.2177590


  • Iterative detection and decoding (IDD)
  • M-algorithm
  • k-best search
  • list sphere decoding
  • look-ahead path metric
  • soft-input soft-output detection
  • tree detection
  • turbo principle

ASJC Scopus subject areas

  • Information Systems
  • Computer Science Applications
  • Library and Information Sciences


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