A method and apparatus for allocating subcarriers in an orthogonal frequency division multiple access (OFDMA) system is described. In one embodiment, the method comprises allocating at least one diversity cluster of subcarriers to a first subscriber and allocating at least one coherence cluster to a second subscriber.

Ofdma with adaptive subcarrier-cluster configuration and selective loading

We present a novel timing offset estimation method for orthogonal frequency division multiplexing systems. The estimator proposed here is designed to avoid the ambiguity which occurs in Schmidl's (1997) timing offset estimation method. The performance of the proposed scheme is presented in terms of mean and mean-square error (MSE) obtained by simulations. The simulation results show that the proposed estimator has a significantly smaller MSE than the other estimators.

A novel timing estimation method for OFDM systems

We present a novel timing offset estimation method for orthogonal frequency division multiplexing(OFDM) systems. The proposed estimator is designed to avoid the ambiguity in timing offset estimation. The performance of proposed scheme is presented in terms of mean and mean-square error (MSE) sense. The simulation results show that the proposed estimator is unbiased and has significantly smaller MSE.

Multi-carrier communications with adaptive cluster configuration and switching

A pilot phase tracking loop for an OFDM receiver including a phase rotator receiving an incoming signal, a fast Fourier transform coupled to a phase rotator output, and a pilot phase error metric including a discrete Fourier transform portion coupled to the phase rotator output. The pilot phase error metric determines a phase error estimate associated with a received OFDM symbol, e.g., a data symbol, from the phase rotator output. A loop filter is coupled to the pilot phase error metric output and an oscillator is coupled to the loop filter output. The oscillator output is coupled to the phase rotator to adjust the phase of subsequent OFDM symbols of the incoming signal. Phase noise introduced by a radio portion of the OFDM receiver and OFDM transmitter is reduced by the baseband portion of the OFDM receiver improving OFDM signal tracking under poor SNR conditions.

Ofdm pilot tone tracking for wireless lan

In this paper, a new carrier frequency offset (CFO) estimator based on the system of estimation of signal parameters via rotational invariance technique is proposed for interleaved orthogonal frequency division multiple access uplink systems. This new estimator performs better in relatively low signal-to-noise region than a CFO estimator recently proposed by Cao and Yao, and has a much lower computational complexity as well. Simulation results show several performance examples for the proposed CFO estimator which demonstrate the advantages of the proposed estimator over the Cao and Yao's version.

Carrier Frequency Offset Estimation Using ESPRIT for Interleaved OFDMA Uplink Systems

We propose a new coarse frequency offset estimation algorithm in orthogonal frequency-division multiplexing systems, which performs robust operation in the presence of a symbol timing offset within an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed, and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. The proposed algorithm adapts the concept of the coherence phase bandwidth for the purpose of weakening the effect of the symbol timing offset.

A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth

In this paper, we investigate an advanced peak windowing method as a peak-to-average power ratio (PAPR) reduction technique in orthogonal frequency division multiplexing (OFDM) systems. The advanced peak windowing method is performed by introducing new weighting coefficients in case that successive peaks are generated within a half of the window length. Applying the new weighting coefficients, we can tightly limit the successive peaks to the given threshold level. Through a computer simulation, we verify that the BER performance improvement can be achieved by the proposed peak windowing method while maintaining almost the same complementary cumulative distribution function (CCDF) and spectral characteristics.

A new PAPR reduction technique for OFDM systems using advanced peak windowing method

A new coarse frequency offset estimation algorithm is proposed which performs robust operation in the presence of a symbol timing offset in an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. In addition, a new technique for performing the coarse frequency estimation using the coherence phase bandwidth is described. Simulation results show that the proposed algorithm estimates a coarse frequency offset well under both AWGN and multipath channels even in the presence of the symbol timing offset within an allowed range.

The bit error probability of the downlink of an MC-CDMA system is analysed taking into account the effect of a carrier frequency offset for Rayleigh and Rician fading channels. Derived results show that the performance of an MC-CDMA system is very sensitive even to a relatively small frequency offset.

Keukjoon Bang

Papers

Carrier Frequency Offset Estimation Using ESPRIT for Interleaved OFDMA Uplink Systems

A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth

A new PAPR reduction technique for OFDM systems using advanced peak windowing method

A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth

Effect of carrier frequency offset on performance of MC-CDMA systems