Selected Mapping Orthogonal Frequency Division Multiplexing Research Articles

Computational complexity reduction of GreenOFDM

The GreenOFDM technique is a new SeLected Mapping Orthogonal Frequency Division Multiplexing (SLM-OFDM) scheme where the same Peak-to-Average Power Ratio (PAPR) reduction is attained at a reduced number of computed IFFTs. Indeed, for the same performance the SLM-OFDM requires computing U IFFTs while the GreenOFDM requires only $2\sqrt {U}$. In this paper, a method specific to the GreenOFDM to further reduce its computational complexity is presented. The results are presented through the probabilistic distributions of the number of computed IFFTs and the total number of operations. The methods being probabilistic, a solution to deal with the induced latency is proposed in order to guarantee real-time operation of the transmitter. Finally, the digital power consumption of the proposed method is proven to be negligible as compared with the High Power Amplifier (HPA) power consumption when implemented in a dedicated processor.

A low complexity SI sequence estimator for pilot-aided SLM–OFDM systems

Selected mapping (SLM) is a well-known method for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. However, as a consequence of implementing SLM, OFDM receivers often require estimation of some side information (SI) in order to achieve successful data recovery. Existing SI estimation schemes have very high computational complexities that put additional constraints on limited resources and increase system complexity. To address this problem, an alternative SLM approach that facilitates estimation of SI in the form of phase detection is presented. Simulations show that this modified SLM approach produces similar PAPR reduction performance when compared to conventional SLM. With no amplifier distortion and in the presence of non-linear power amplifier distortion, the proposed SI estimation approach achieves similar data recovery performance as both standard SLM–OFDM (with perfect SI estimation) and also when SI estimation is implemented through the use of an existing frequency-domain correlation (FDC) decision metric. In addition, the proposed method significantly reduces computational complexity compared with the FDC scheme and an ML estimation scheme.

Performance Evaluation of a Low Complexity Row-Column Transform Approach for SLM Based OFDM Transmission System

Selected mapping (SLM) technique is commonly employed for reducing peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Conventional SLM scheme has better spectral efficiency, but requires a bank of inverse fast Fourier transforms (IFFTs) to produce candidate signals, resulting in a dramatic increase in computational complexity. To reduce the computational complexity of the SLM technique, this paper proposes a new PAPR reduction scheme of OFDM system, called a modified fast T-transform based SLM OFDM scheme, which considerably reduces the computational complexity with better PAPR reduction performance compared to the conventional T-SLM OFDM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16d standard. For the OFDM system with 256 subcarriers, the proposed scheme can reduce the complex multiplications by 68.7 % with the lower PAPR by range of 7 dB which is about 1 dB less than the conventional SLM based OFDM.

A low complexity selective mapping OFDM using multiple IFFT stages

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 using a radix Decimation In Time (DIT) or Decimation In Frequency (DIF) IFFT algorithm are used to generate the phase sequences. It is shown that DIF provides lower 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 a low radix algorithm. We further reduce the computational complexity by proposing a low computational complexity technique based on multiplying the phase sequences at multiple 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.

Turbo Coded OFDM for Reducing PAPR and Error Rates

A selective-mapping (SLM) scheme which does not require the transmission of side information and can reduce the peak to average power ratio (PAPR) in turbo coded orthogonal frequency-division multiplexing (OFDM) systems is proposed. The candidates of the proposed SLM are respectively generated by a turbo encoder using various interleavers. The waiver of side information can avoid the degradation of error rate performance which results from the incorrect recovery of side information at receiver in the conventional SLM OFDM system.

Optimality Condition for Selected Mapping in OFDM

It is well known that orthogonal-frequency-division-multiplexing (OFDM) transmission is spectrally efficient but power inefficient due to the large peak-to-average power ratio (PAR) of the OFDM signal. Selected mapping (SLM) is a promising PAR reduction technique that is distortionless and has good PAR reducing capability. In SLM, the phases of the frequency domain OFDM subsymbols are first rotated before the inverse Fourier transform is applied; thus, an equivalent representation of the OFDM signal can be obtained. The one with the lowest PAR from among M such representations is retained and transmitted in place of the original OFDM signal. In this paper, we investigate the optimum design of the phase rotation table so that the complementary cumulative distribution function (CCDF) of the PAR of the SLM OFDM signal is minimized for any given M. We prove that if the phases (denoted by random variable phi) are independently and identically distributed (i.i.d.) with E[ejphi]=0, then optimum SLM performance can be achieved

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 SLM OFDM scheme with low complexity for PAPR reduction

The authors introduce a new selected mapping (SLM) orthogonal frequency division multiplexing (OFDM) scheme with low computational complexity. The proposed SLM scheme transforms an input symbol sequence into a set of OFDM signals by multiplying the phase sequences to the signal after a certain intermediate stage of inverse fast Fourier transform (IFFT). Then, the OFDM signal with the lowest peak-to-average power ratio (PAPR) is selected for transmission. The new SLM OFDM scheme reduces the computational complexity, while it shows almost the same performance of PAPR reduction as that of the conventional SLM OFDM scheme.