Turbo equalization of doubly selective channels

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2 Citations (Scopus)


In this paper, turbo equalization for transmission over doubly selective channels is proposed. The maximum a posteriori probability (MAP) algorithm is used for channel detection as well as for channel decoding. The detection/decoding constituents can exchange soft information in an iterative manner resulting in the so-called turbo equalization. The time-varying multi-path fading channel is modeled using the basis expansion model (BEM). In this BEM, the time-varying channel is viewed as a bank of time-invariant finite impulse response filters, and the time variation is captured by means of time-varying complex exponential basis functions. Therefore, the time-varying transition tables that characterize the time-varying channel can also follow a similar BEM. The complexity of the MAP channel detector is rather prohibitive for practical applications. This motivates the search for lower-complexity soft-output channel detectors. For this purpose, soft-output linear minimum-mean square error (LMMSE)-based channel detectors are proposed for single carrier as well as for multi-carrier systems. With the use of Gaussian approximation, expressions for the a posteriori and extrinsic log-likelihood ratios have been derived. The performance of the proposed turbo equalization schemes are evaluated using numerical simulations.

Original languageEnglish
Pages (from-to)1691-1703
Number of pages13
JournalWireless Communications and Mobile Computing
Issue number18
Publication statusPublished - Dec 25 2014


  • MAP
  • OFDM
  • doubly selective channels
  • single carrier
  • soft-input soft-output
  • turbo equalization

ASJC Scopus subject areas

  • Information Systems
  • Computer Networks and Communications
  • Electrical and Electronic Engineering


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