Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

OFDM and Its Wireless Applications: A Survey

The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

On the synchronization techniques for wireless OFDM systems

A new decision-directed (DD) synchronization scheme is proposed for joint estimation of carrier frequency offset (CFO) and sampling clock frequency offset (SFO) in orthogonal frequency-division multiplexing (OFDM) systems. By exploiting the hard decisions, we report accurate estimators of residual CFO and small SFO. The performance analysis and simulation results indicate that the proposed novel DD scheme achieves much better performance than the conventional pilot-based schemes in both additive white Gaussian noise and frequency-selective channels.

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Decision-directed fine synchronization in OFDM systems

This work presents an algorithm for joint estimation of carrier-frequency offset and timing offset for orthogonal frequency-division multiplexing (OFDM) systems in the tracking mode. The proposed weighted least-squares algorithm derives its estimates based on phase differences in the received pilot subcarrier signals between two symbols. Moreover, the optimal weights in two different channel conditions are derived. Both analysis and simulation show that the weighted least-squares algorithm can effectively and accurately estimate the carrier-frequency offset as well as the timing offset of OFDM signals in multipath fading channels.

Joint weighted least-squares estimation of carrier-frequency offset and timing offset for OFDM systems over multipath fading channels

Presenting the state of the art in broadband wireless access technology, this unique resource methodically presents the fundamentals of OFDM(A) technology--the cornerstone of the next generation of broadband wireless access offerings. In addition, this book succinctly depicts the future landscape of mobile broadband wireless access and the standards developed by the IEEE 802.16 standards organization. The book gives you a solid understanding of the essential features of IEEE 802.16d (fixed) and 802.16e (mobile) and the role of the WiMAX Forum in defining interoperability and certification criteria. This comprehensive resource discusses important requirements, tradeoffs, and other critical design considerations, providing a full overview of the issues and possible solutions for your work in the field. Offering practical, end-to-end guidance, this book serves as your one-stop reference to cutting-edge broadband wireless access systems.

OFDM Towards Fixed and Mobile Broadband Wireless Access

This paper discusses the effects of time synchronization errors on OFDM (orthogonal frequency division multiplexing) digital communications. Time synchronization consists of symbol timing recovery and sampling clock adjustment. In general, symbol timing recovery is carried out before sampling clock adjustment. The main problem with time synchronization errors is that the sample rob/stuff phenomenon due to sampling clock frequency offset leads to adding the symbol timing offset. Thus a more efficient synchronization algorithm is required. This paper introduces a new joint algorithm between symbol timing recovery and sampling clock adjustment using the difference of phase changes between the pilot carriers. The performance of the proposed algorithm is carried out under AWGN and multipath fading channel.

Sang Hyun Do

Papers

A new joint algorithm of symbol timing recovery and sampling clock adjustment for OFDM systems