A. Ghassemi

PAPR reduction of OFDM using PTS and error-correcting code subblocking - Transactions Papers

Partial transmit sequence (PTS) is a proven technique to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It achieves considerable PAPR reduction without distortion, but the high computational complexity of multiple Fourier transforms is a problem in practical systems. To address the complexity, signals at the middle stages of an ¿-point radix FFT using decimation in frequency (DIF) are employed for PTS subblocking. We formulate OFDM symbols based on these signals to exploit the periodic autocorrelation function (ACF) of the vectors in the PTS subblock partitioning. Error-correcting codes (ECCs) are employed in the subblocking for the PTS radix FFT. This new technique significantly decreases the computational complexity while providing comparable PAPR reduction to ordinary PTS (O-PTS), even with a small number of stages after PTS partitioning. Numerical results are presented which confirm the PAPR improvements.

A Low Complexity SLM-Based Radix FFT Method for PAPR Reduction in OFDM Systems

A low complexity selective mapping (SLM) technique for reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal is introduced. The intermediate signals within an N-point IFFT are used to generate the phase sequences. We use decimation in frequency (DIF) and propose a low computational complexity technique based on multiplying the phase sequences at different IFFT stages. This new technique greatly reduces the multiplicative complexity while providing similar PAPR reduction to ordinary SLM (O-SLM). The additive complexity is also reduced.

SLM-Based Radix FFT for PAPR Reduction in OFDM Systems

A radix FFT-based selective mapping (SLM) technique for reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal is introduced. The intermediate signals within an N-point IFFT using a radix decimation in time (DIT) or decimation in frequency (DIF) IFFT algorithm are used for multiplying the phase sequences. Multiple IFFTs are then applied to the remaining stages. It is shown that DIF provides low multiplicative complexity in generating the SLM sequences compared to DIT, with the same PAPR reduction. In addition, a high radix FFT algorithm provides better PAPR reduction performance per stage with less multiplicative complexity compared to low radix algorithms.

PTS Peak Power Reduction of OFDM Signals with Low Complexity IFFTs

Partial transmit sequence (PTS) is a distortionless technique used to reduce the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. However, it has a relatively high computational complexity due to the computation of multiple inverse fast Fourier transforms (IFFTs). We reduce this complexity by using a radix FFT that computes multiple IFFTs with low computational complexity. Signals at the middle stages of an N-point radix-r FFT using decimation in frequency (DIF) are employed for PTS subblocking. Performance results are presented which show that PAPR reduction similar to other techniques such as ordinary PTS (O-PTS) is achieved.

A Simplified Suboptimal Algorithm for Tone Reservation OFDM

A gradient algorithm has been used in the tone reservation technique for peak to average power ratio (PAPR) reduction. This provides a good approximation to the optimal solution with lower complexity. This technique requires that a kernel signal be computed and iteratively shifted in the time-domain to the peak locations to reduce the PAPR. The kernel signal should be updated dynamically for the best performance in time varying channels, which increases the computational complexity. In this paper, we propose a low complexity gradient algorithm for computing the peak reduction kernels. This approach is more efficient than the previous algorithm, and provides better PAPR performance.

Fractional Selective Mapping Using Decimation in Time IFFT/FFT

An IFFT-based selective mapping (SLM) technique is presented for reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. We use fractional inputs at intermediate stages within a decimation in time (DIT) IFFT to generate the SLM sequences. This significantly reduces the computational complexity while maintaining a PAPR performance close to that with original SLM. This new technique provides a better PAPR versus complexity tradeoff compared to previous techniques. Further, this approach provides similar complexity reduction for both low and high radix IFFT algorithms.

Low Autocorrelation Fractional PTS Subblocking for PAPR Reduction in OFDM Systems

Partial transmit sequence (PTS) is a distortionless technique used to reduce the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. However, PTS has a relatively high computational complexity due to the computation of multiple inverse fast Fourier transforms (IFFTs). To reduce this complexity, fractional subblocking was introduced where a subset of inputs to identical inverse discrete Fourier transforms (IDFTs) (within an N-point IFFT) were used for subblocking. Unfortunately, the PAPR performance is degraded as the number of identical DFTs is increased. In this paper, we exploit the periodic autocorrelation function (ACF) of the PTS sequences to improve the PAPR performance with fractional subblocks. We show that a PAPR reduction is achieved which is better than with pseudo-random subblocking.

Intercarrier interference reduction in OFDM systems using low complexity selective mapping

Selective mapping (SLM) has been employed to reduce the peak interference-to-carrier ratio (PICR) in OFDM systems. Here, we significantly reduce the computational complexity of SLM using subsets of intermediate signals within the inverse fast Fourier and fast Fourier transforms, while achieving performance close to that previously obtained.

Fractional Subblocking for Partial Transmit Sequence OFDM

Partial transmit sequence (PTS) is a well known technique used to reduce the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. However, it has relatively high complexity due to the computation of multiple inverse fast Fourier transforms (IFFTs). To reduce this complexity, we use intermediate signals within a decimation in frequency (DIF) radix IFFT and propose a new PTS subblocking technique which requires the computation of only partial IFFTs. Performance results are presented which show a PAPR reduction similar to that with other techniques such as original PTS (O-PTS). Further, we show that complexity reduction can be achieved with either low or high radix IFFT algorithms.

Decoupled Phase Optimization for Partial Transmit Sequence OFDM

Partial transmit sequence (PTS) is a proven technique for peak-to-average-power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. Determining the optimal phase factors requires an exhaustive search over all possible sets of phase factors. Hence, simplified optimal and suboptimal approaches have been proposed. Previous methods of formulating the phase factor optimization have considered variables over the entire OFDM symbol. With no degradation in performance, we show that fractional PTS sub-blocking can reduce the number of variables in the optimization problem. It can easily be employed with other techniques to significantly reduce complexity.