Seok-Joong Heo

A new PTS OFDM scheme with low complexity for PAPR reduction

In this paper, we introduce a new partial transmit sequence (PTS) orthogonal frequency division multiplexing (OFDM) scheme with low computational complexity. In the proposed scheme, 2/sup n/-point inverse fast Fourier transform (IFFT) is divided into two parts. An input symbol sequence is partially transformed using the first l stages of IFFT into an intermediate signal sequence and the intermediate signal sequence is partitioned into a number of intermediate signal subsequences. Then, the remaining n-l stages of IFFT are applied to each of the intermediate signal subsequences and the resulting signal subsequences are summed after being multiplied by each member of a set of W rotating vectors to yield W distinct OFDM signal sequences. The one with the lowest peak to average power ratio (PAPR) among these OFDM signal sequences is selected for transmission. The new PTS OFDM scheme reduces the computational complexity while it shows almost the same performance of PAPR reduction as that of the conventional PTS OFDM scheme.

An overview of peak-to-average power ratio reduction schemes for OFDM signals

Orthogonal frequency division multiplexing (OFDM) has been adopted as a standard for various high data rate wireless communication systems due to the spectral bandwidth efficiency, robustness to frequency selective fading channels, etc. However, implementation of the OFDM system entails several difficulties. One of the major drawbacks is the high peak-to-average power ratio (PAPR), which results in intercarrier interference, high out-of-band radiation, and bit error rate performance degradation, mainly due to the nonlinearity of the high power amplifier. This paper reviews the conventional PAPR reduction schemes and their modifications for achieving the low computational complexity required for practical implementation in wireless communication systems.

On the phase sequence set of SLM OFDM scheme for a crest factor reduction

The crest factor distribution of orthogonal-frequency-division-multiplexing (OFDM) symbol sequences is evaluated, and it is shown that OFDM symbol sequences with a short period are expected to have a high crest factor. The crest factor relationship between two input symbol sequences, Hamming distance D apart, is also derived. Using these two results, two criteria are proposed for a phase sequence set of the selected mapping (SLM) OFDM scheme and suggest the rows of the cyclic Hadamard matrix constructed from an m-sequence as a near-optimal phase sequence set of the SLM OFDM scheme.

A New Blind SLM Scheme With Low Decoding Complexity for OFDM Systems

In this paper, a new blind selected mapping (BSLM) scheme is proposed for orthogonal frequency division multiplexing systems. The proposed BSLM scheme embeds the side information identifying a phase sequence into itself by giving the optimal phase offset to the elements of each phase sequence, which are determined by the biorthogonal vectors for the partitioned subblocks. When U phase sequences and maximum likelihood decoder are used, the proposed BSLM scheme reduces the decoding complexity by (U-2)/U compared with the conventional BSLM scheme. Also, pairwise error probability (PEP) analysis for the proposed BSLM scheme is performed over the fading channel. Based on the PEP analysis, the bit error rate (BER) performance of the proposed BSLM scheme is shown to be determined by the subblock partitioning and phase offset. Finally, it is shown that for QPSK and 16-QAM, the detection failure probability and the BER of the proposed BSLM scheme are almost the same as those of the conventional BSLM scheme through numerical analysis.

A Modified SLM Scheme with Low Complexity for PAPR Reduction of OFDM Systems

In this paper, we propose a new peak-to-average power ratio (PAPR) reduction scheme of orthogonal frequency division multiplexing (OFDM) system, called a modified selected mapping (SLM) scheme, which considerably reduces the computational complexity with keeping the similar PAPR reduction performance compared with the conventional SLM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16 standard. For the OFDM system with 2048 subcarriers, the proposed scheme with 4 binary phase sequences can reduce the complex multiplications by 63.5% with the similar PAPR reduction compared with the SLM scheme with 16 binary phase sequences.

Analysis of PAPR reduction performance of SLM schemes with correlated phase vectors

The peak to average power ratio (PAPR) reduction performance depends on the phase vectors of selected mapping (SLM) scheme where the alternative input symbol vectors are generated by multiplying an input symbol vector by phase vectors. Thus, the symbol powers of alternative orthogonal frequency division multiplexing (OFDM) signals obtained by inverse Fourier transforming the alternative input symbol vectors become correlated. In this paper, the relationship between the correlations of component powers of alternative OFDM signal vector and the correlations of phase vectors are evaluated. Then, the complementary cumulative distribution function (CCDF) of PAPR in SLM scheme is derived using multivariate gamma distribution. The derived CCDF coincides exactly with the simulation result for peak reduced OFDM system with SLM.

A New Blind SLM Scheme with Low Complexity of OFDM Signals

In this paper, we propose a new blind SLM scheme with low complexity using m-sequence as a phase sequence in OFDM. The proposed scheme significantly reduces the compu- tational complexity for searching the side information of the phase sequence and decoding the alternative symbol sequence at the receiver. After generating alternative symbol sequences using a set of phase sequences, the side information for each alternative symbol sequence is embedded in it through block partitioning and phase rotation. The proposed method does not need additional inverse fast Fourier transform (IFFT) and has the same PAPR reduction performance compared to the conventional SLM scheme. In order to find the side information, a maximum likelihood (ML) decoder with lower complexity is derived, which guarantees lower detection failure probability of side information compared to the conventional blind SLM scheme.

Construction of the Near Optimal PRT Set using the Cyclic Difference Set in TR Scheme

In the tone reservation (TR) scheme, it is known that the set of randomly selected peak reduction tones (PRTs) performs better than the contiguous PRT set and the interleaved PRT set in the PAPR reduction of orthogonal frequency division multiplexing (OFDM) signals. It is also known that finding the optimal PRT set is equivalent to solving the secondary peak minimization problem in the TR scheme. However, this problem cannot be solved for the practical number of tones because choosing k tones out of N subcarriers requires O(k) computational complexity. In this paper, the near optimal PRT set of the TR scheme is proposed, which is constructed from the cyclic difference set.

A PTS OFDM scheme with low computational complexity

In this paper, we introduce a new partial transmit sequence (PTS) orthogonal frequency division multiplexing (OFDM) scheme with low computational complexity. In the proposed scheme, 2n - point inverse fast Fourier transform (IFFT) is divided into two parts. An input symbol sequence is partially transformed using the first l stages of IFFT to generate an intermediate signal sequence and the intermediate signal sequence is partitioned into a number of intermediate signal subsequences. Then, the remaining n - l stages of IFFT are applied to each of the intermediate signal subsequences and the resulting signal subsequences are summed after being multiplied by each member of a set of W rotating vectors to yield W distinct OFDM signal sequences. The one with the lowest peak to average power ratio (PAPR) among these OFDM signal sequences is selected for transmission. The new PTS OFDM scheme reduces the computational complexity while it shows almost the same performance of PAPR reduction as that of the conventional PTS OFDM scheme

Partial Bit Inverted SLM Scheme for PAPR Reduction in QAM Modulated OFDM Signals

In this paper, we propose a new selected mapping (SLM) scheme for reducing peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals modulated with quadrature amplitude modulation (QAM), called partial bit inverted SLM (PBISLM). The proposed scheme changes the magnitudes as well as the phases of QAM symbols by applying binary phase sequences to the binary data sequence before mapped to QAM symbols. Simulation results show that the proposed scheme has better PAPR reduction performance than the conventional SLM scheme for the QAM modulated OFDM signals, especially for the small number of subcarriers.