Iterative Channel Estimation and Decoding of Turbo Coded SFBC-OFDM Systems

• Published in: IEEE transactions on wireless communications Vol. 6; no. 8; pp. 3090 - 3101
• Main Authors: Dogan, Hakan, Cirpan, Hakan A., Panayirci, Erdal
• Format: Journal Article
• Language: English
• Published: Piscataway, NJ IEEE 01.08.2007; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Channel estimation; Channels; Computer errors; Computer simulation; Decoders; EM algorithm; Error analysis; Error detection; Exact sciences and technology; Fading; Frequency; Iterative algorithms; Iterative decoding; Iterative methods; MAP channel estimation; Maximization; Mean square errors; OFDM; OFDM systems; Orthogonal Frequency Division Multiplexing; Random processes; Receivers; space-frequency coding; Studies; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Turbo codes; turbo receiver; Performance evaluation; Block code; Parameter estimation; Bit error rate; MAP channel estimation; Iterative method; turbo receiver; Stochastic process; Mean square error; Selective fading; Estimator efficiency; Frequency selection; Channel estimation; Series expansion; Signal detection; Fading channels; Estimation error; Karhunen Loeve transformation; Computer simulation; Turbo code; Decoding; Computational complexity; OFDM systems; Orthogonal frequency division multiplexing; space-frequency coding; EM algorithm
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2007.06006

We consider the design of turbo receiver structures for space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems in the presence of unknown frequency and time selective fading channels. The Turbo receiver structures for SFBC-OFDM systems under consideration consists of an iterative MAP Expectation/Maximization (EM) channel estimation algorithm, soft MMSE-SFBC decoder and a soft MAP outer-channel-code decoder. MAP-EM employs iterative channel estimation and it improves receiver performance by re-estimating the channel after each decoder iteration. Moreover, the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The optimal truncation property of the KL expansion can reduce computational load on the iterative estimation approach. The performance of the proposed approaches are studied in terms of mean square error and bit-error rate. Through computer simulations, the effect of a pilot spacing on the channel estimator performance and sensitivity of turbo receiver structures on channel estimation error are studied. Simulation results illustrate that receivers with turbo coding are very sensitive to channel estimation errors compared to receivers with convolutional codes. Moreover, superiority of the turbo coded SFBC-OFDM systems over the turbo coded STBC-OFDMsystems is observed especially for high Doppler frequencies.