Carrier Frequency Offset Mitigation in Asynchronous Cooperative OFDM Transmissions

• Published in: IEEE transactions on signal processing Vol. 56; no. 2; pp. 675 - 685
• Main Authors: Li, Xiaohua, Ng, Fan, Han, Taewoo
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Applied sciences; Bandwidth; Carrier frequencies; Carrier frequency offset (CFO); Coding, codes; cooperative transmissions; Degradation; Efficiency; Encoding; Exact sciences and technology; Fast Fourier transforms; Fourier transforms; Frequency division multiplexing; Information, signal and communications theory; Multiplexing; OFDM; Offsets; Orthogonal Frequency Division Multiplexing; orthogonal frequency-division multiplexing (OFDM); Performance loss; Power efficiency; Preprocessing; Propagation losses; Signal and communications theory; Spread spectrum communication; synchronization; Telecommunications and information theory; Transmitters; Performance evaluation; Fast Fourier transformation; Transmitter; Decoding; Synchronization; Algorithm; Implementation; Carrier frequency; Algorithm performance; Coding; Critical frequency; Orthogonal frequency division multiplexing; Carrier frequency offset (CFO); Spread spectrum; Frequency offset; cooperative transmissions; orthogonal frequency-division multiplexing (OFDM); Asynchronous transmission
• ISSN: 1053-587X; 1941-0476
• DOI: 10.1109/TSP.2007.907820

Carrier frequency offset (CFO) mitigation is critical for orthogonal frequency-division multiplexing (OFDM)-based cooperative transmissions because even small CFO per transmitter may lead to severe performance loss, especially when the number of cooperative transmitters is large. In this paper, we show that cyclic prefix (CP) can be exploited to mitigate or even remove completely the CFO. The mitigation performance increases along with the CP length. In particular, long CP with length proportional to NI , where N is the fast Fourier transform (FFT) block length and I is the number of cooperative transmitters, can guarantee a complete CFO removal. While this comes with a reduction in bandwidth efficiency, the long CP in the proposed scheme is exploited to enhance transmission power efficiency in a way similar to spread-spectrum systems, and thus is different from conventional CP that degrades both bandwidth and power efficiency. An efficient CFO-mitigation algorithm is developed that has complexity at most O( NI 2 ), or even linear in N approximately in some cases. Implemented as a preprocessing procedure independently from cooperative encoding/decoding details, this algorithm makes the CFO problem effectively transparent to and thus has general applications in OFDM-based transmissions.