Peak to Average Power Ratio Reduction in NC–OFDM Systems

Abstract

Non contiguous orthogonal frequency division multiplexing (NC-OFDM) is an efficient and adaptable multicarrier modulation scheme to be used in cognitive radio communications. However like OFDM, NC-OFDM also suffers from the main drawback of high peak to average power ratio (PAPR). In this paper PAPR has been reduced by employing three different trigonometric transforms. Discrete cosine transform (DCT), discrete sine transform (DST) and fractional fourier transform (FRFT) has been combined with conventional selected level mapping (SLM) technique to reduce the PAPR of both OFDM and NC-OFDM based systems. The method combines all the transforms with SLM in different ways. Transforms DCT, DST and FRFT have been applied before the SLM block or inside the SLM block before IFFT. Simulation results show the comparative analysis of all the transforms using SLM in case of both OFDM and NC-OFDM based systems.

A Review of Partial Transmit Sequence for PAPR Reduction in the OFDM Systems

“…Also, the DFT-spread technique [72], the Discrete Hartley Transform (DHT)-spread technique [73] and single carrier frequency division multiplexing (SC-FDM) technique [74], [75] are utilized with OFDM for reducing the PAPR value effectively in an intensity modulation and direct detection (IM/DD) optical systems. Furthermore, the DFT-spread with PTS has been introduced for further PAPR reduction in the OFDM system [76], as well as, the Discrete cosine transform (DCT)spread is combined with the PTS technique for reducing the PAPR value without requiring side information [77], [78].…”

“…The DFT-spread is a linear process, and it can reduce the autocorrelation among the subcarriers by expanding the frequency domain signal [76]. Owing to the association of the PAPR values with the autocorrelation function, the PAPR value can be reduced by using the DFT-spread method [77]. The principle idea of the DFT-S-PTS is to partition the data block X into non-overlapping subblocks, and then the partitioned subblocks are applied to the bank of DFT-S to generate the transformed sequences.…”

“…The discrete cosine transforms spread-PTS technique (DCT-S-PTS) [78] was proposed based on applying the discrete cosine transform spread to the PTS techniques in the frequency domain. This method reduces the PAPR value in the OFDM system, where the DCT unit works to reduce the autocorrelation among the subcarriers on each subblock in the frequency-domain and this leads to reducing the PAPR value [77]. The data sequence X is passed to the DCT block, which extend the input data sequence so that the autocorrelation among the subcarriers is reduced.…”

A powerful PTS strategy boosted by a novel discrete crow search algorithm for reducing the PAPR of UFMC signals

“…Besides, high connectivity and reliability are another important two requirements to enable the use of aforementioned applications in incredible diversity [1][2][3][4]. Endless technological developments and increasing demands in parallel with this have urged the researchers to develop alternative waveforms to be employed in 5G and beyond cellular technologies since the orthogonal frequency division multiplexing (OFDM) [5,6] actively used in 4G long term evolution (LTE) physical layer as a basic waveform barely handles these growing demands due to its shortcomings like poor spectral efficiency, the requirement of synchronization and sensitivity to frequency and time offsets. For this reason, a novel waveform named universal filtered multicarrier (UFMC) with unique qualifications was proposed by Vakilian et al [7].…”