Combining partial transmit sequences and selective mapping to reduce computational complexity of selective mapping techniques

OFDM (orthogonal frequency division multiplexing) is widely used in 4th generation applications owing to its robustness in fading environments. The major issues with OFDM systems is the high PAPR (peak-to-average power ratio) of the transmitted signals, it leads to in and out of band distortion. SLM (selective mapping) and PTS (partial transmit sequence) are two key methods for PAPR reduction. Both the methods require exhaustive searching of phase factors to optimize the PAPR, these searches lead to high computational complexity. This paper discusses using optimization based PAPR reduction methods which an be used with PTS for the reduction of computational complexity and search space. In this paper we have analyzed PTS and SLM with particle swarm optimization (PSO), Artificial Bee Colony (ABC) and differential evolution (DE). PAPR and BER (bit error rate) comparison is done for both the cases.

Orthogonal Frequency Division Multiplexing (OFDM) is typically a system used in encoding digital data. It has huge benefits among which primary are high spectral efficiency upon Inter Symbol Interference (ISI) and robustness. It also has some drawbacks, the main hitch in OFDM system is High Peak to Average Power Ratio (PAPR). In order to minimize PAPR, many techniques are available among which some common and efficient are Partial Transmit Sequence (PTS), Selected Mapping (SLM), Coding, Interleaving, Companding, Peak windowing, Peak reduction, Envelope Scaling. Every method has both edge and snag. The simplest is clipping. There are also some complex techniques like PTS, SLM. In this paper the proposed method is a hybrid combination of Repeated Frequency Domain Filtering and Clipping (RFDFC) and Absolute Exponential Companding (AEC). This method not only bring PAPR to 3.5 dB as compared to 10.5 dB in original, but is also easy to implement.

Orthogonal frequency division multiplexing (OFDM) is the advanced transmission scheme utilized in 4G. Nevertheless, it has several shortcomings like guard band, peak-to-average power ratio (PAPR), high power consumption, incapable to accommodate various other devices (an IOT application). Hence, OFDM cannot be considered in 5G due to the several disadvantages mentioned above. Filter bank multi-carrier (FBMC) is believed to be one of the most promising technologies which can be used in 5G. FBMC and OFDM are multi-carrier system. It is obvious that it agonizes from PAPR which hamper the efficiency of the system. The conventional peak reduction methods utilized in OFDM cannot be used in FBMC due to the overlapping structure of FBMC. In this work, a novel selective mapping (SLM) and partial transmit sequence (PTS) PAPR reduction technique is suggested for FBMC. The proposed techniques are implemented by using an elementary successive optimization technique that upsurge the PAPR performance and ensure the design difficulty is taken low. PAPR and bit error rate (BER) parameters are analyzed and simulated for the proposed and conventional PAPR reduction techniques. The simulation results show that the SLM and PTS accomplished an excellent PAPR reduction up to 2.8 and 4.8 dB as compared to other peak power minimization techniques.

Selected Mapping (SLM) and Partial Transmit Sequence (PTS) are two very well-known Peak-to-average Power Ratio (PAPR) reduction techniques for Orthogonal Frequency Division Multiplexing (OFDM) systems. Both these schemes show good PAPR reduction capabilities. However, for any PAPR reduction technique, the nature of spectral occupancy and the associated computational complexity also need to be taken into account when the overall performance is considered. In this paper, our goal is to perform a comparative performance analysis of SLM and PTS techniques by considering these three parameters, i.e. PAPR reduction, computational overhead and spectral compactness. For this, we at first look for the optimum values in terms of number of sequences in SLM and no. of sub-blocks in PTS. And then based on this finding, we perform performance analysis. Our finding shows that, PTS outperforms SLM when compared on the parameters mentioned above. Finally, to explore the feasibility of further improvement, we apply Walsh-Hadamard Transform to PTS scheme and show that it further reduces PAPR and improves spectral compactness.

The technology has been growing rapidly in the form of portable wireless devices that can perform multiple functions to cope with the state-of-the-art technology and synchronization. A total device capacity must be increased to accommodate new wireless applications. This can be achieved by leveraging new technologies, with higher data rates. Spectrum pooling has gained immense popularity, with increased demand for frequency range and bandwidth availability constraints. Statistics suggest that much of the spectrum licensed is not used all the time. Because of the transmitter's nonlinearity nature, the large (peak to average power ratio (PAPR)) phenomenon is a drawback in orthogonal frequency division multiplexing (OFDM). Several hybrid approaches have recently been implemented to minimize PAPR's high value, at the expense of increasing the level of computational complexity in the system. In this paper, a new hybrid approach has been introduced in parallel to combine the selective mapping approach (SLM) with the partial transmit sequence (PTS) approach to improve the efficiency of PAPR reduction with lower numerical method complexity. The findings reveal that the OFDM systems with the proposed hybrid approach have better efficiency in terms of PAPR elimination, side-information, and computational complexity compared to current hybrid methods. Also, a hybrid approach proposed output could be maintained without degradation. Index Terms: OFDM, PTS, PAPR, SLM

In wireless communication, parallel transmission of symbols using multi carriers is applied to achieve high efficiency in terms of throughput and better transmission quality. Orthogonal Frequency Division Multiplexing (OFDM) is one of the techniques for parallel transmission. In multipath environment the performance of orthogonal frequency division multiplexing (OFDM) is improved by introducing some kind of channel coding. Coded OFDM (COFDM) is the new candidate for application such as DAB and DVB-T due to its better performance in fading environment. However high peak to average power ratio (PAPR) is a major demerit of OFDM system, it leads to increased complexity of circuit and reduced efficiency of RF amplifier. In this paper our aim is to evaluate the PAPR of COFDM system and reducing its effect by clipping, Selected Mapping (SLM) and Partial Transmit Sequence (PTS) techniques. COFDM system used here comply with IEEE 802.11a specifications and Reed Solomon (RS) codes along with convolution codes are used for channel coding purpose. Channel used for consideration is AWGN. The performance is evaluated in terms of PAPR value and BER.

OFDM (Orthogonal Frequency Division Multiplexing) 시스템에서 SLM (Selected Mapping)은 전송신호의 왜곡 없이 PAPR (Peak-to-Average Power Ratio)을 효율적으로 줄일 수 있는 기법이다. 하지만, 충분한 후보 OFDM 신호를 생성하기 위해서는 많은 양의 IFFT (Inverse Fast Fourier Transform) 연산을 필요로 하고, 이는 SLM 기법을 매우 복잡하게 만든다. 따라서 본 논문에서는 첫 번째 후보 OFDM 신호를 변환하여 나머지 IFFT 연산들을 대체하는 새로운 SLM 기법을 제안한다. 제안된 기법은 기존의 SLM 기법과 비교하여 거의 같은 PAPR 저감 성능을 보임과 동시에 계산 복잡도는 크게 감소 시킬 수 있다. SLM (Selected Mapping) is an efficient PAPR (Peak-to-Average Power Ratio) reduction scheme without transmitted signal distortion in OFDM (Orthogonal Frequency Division Multiplexing) systems. However, enormous IFFTs (Inverse Fast Fourier Transforms) are needed to generate sufficient candidate OFDM signals, which cause the SLM to become quite complex. In this paper, we propose a new SLM scheme that replaces the IFFT operations with a conversion of the first candidate OFDM signal. The proposed scheme significantly reduces computational complexity, while it shows almost the same PAPR performance as the conventional SLM scheme.

Particle swarm optimization (PSO) is a swarm intelligence based computer algorithm that is used to find a solution in the search space of an optimization problem. Adding frequency diversity, through subcarrier redundancy, in orthogonal frequency-division multiplexing (OFDM) is a popular approach to improve the robustness of the system. However, frequency redundant OFDM system is prone to high peak-to-average power ratio (PAPR), due to the fact that the same source information is transmitted on multiple subcarriers. Existing schemes such as Selective Mapping (SLM) and partial transmit sequence (PTS) are effective but difficult to implement due to the high computation complexity. In this paper, we propose a two stage PAPR reduction method. We analyze the computational complexity and extensive simulations on the PAPR and show that our scheme considerably reduces the computational complexity while achieving similar PAPR reduction as SLM and better PAPR reduction than PTS.

In this paper, we propose a new PAPR reduction by using a partial transmit sequences (PTS) method with coded side information (SI) technique. These methods are used in an orthogonal frequency division multiplexing (OFDM) system. The OFDM employs orthogonal sub-carriers for data modulation. These sub-carriers unexpectedly present a large peak to average power ratio (PAPR) in some cases. In order to reduce PAPR, the sequence of input data is partitioned into disjoint sub-block of PTS. If number of sub-block increases, high efficiency of PAPR reduction can be obtained. However, a quite large calculation cost must be demanded and thus it is impossible to obtain the optimum PTS. In the proposed method, we introduce a coded side information technique assuming the pseudo-optimum condition into the PTS. The total calculation cost becomes drastically reduced and side information bits for recovering original data in demodulation. In simulation results, the proposed method demonstrated the improvement of PAPR and bit error rate (BER) performance.

This paper proposes a partial transmit sequence (PTS) scheme with applying a stochastic optimization technique for peak-to-average power ratio (PAPR) reduction in the orthogonal frequency division multiplexing (OFDM) system. PTS technique combining can improve the PAPR statistics of an OFDM signals, but the considerable computational complexity for the required search through a high-dimensional vector space is a potential problem for implementation in the practical systems. Differential evolution (DE) is an efficient and powerful population-based stochastic search technique for solving optimization problems over continuous space, which has been widely applied in many scientific and engineering fields. Thus, to reduce the complexity for searching phase weight vector and to improve the PAPR statistics, we introduce the DE, an effective algorithm that solves various combinatorial optimization problems, to search the optimal phase weight factors. The simulation results show that the proposed DE-based PTS obtains the excellent PAPR performance with a low computational complexity.

In this paper, we propose a genetic-simulated annealing algorithm (GSAA) with partial transmit sequence (PTS) technique (GSAA-PTS) to reduce the peak-to-average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) system. Genetic algorithm based PTS method (GA-PTS) is a novel and suboptimal PAPR reduction approach, which has lower computational load than original PTS method. However, researchers still focus on how to improve the PAPR performance. The proposed method GSAA-PTS takes the advantages of genetic algorithm and simulated annealing algorithm to search the best phase factors of PTS. In this method, we initialize the population firstly, and then selection, crossover and mutation are used to generate the new population, finally using the simulated annealing algorithm to update each chromosome in the population. The simulation results show that the better performance of PAPR have been achieved by adopting GSAA-PTS scheme.

A three-dimensional (3D) orthogonal frequency division multiplexing (OFDM) system with peak-to-average power ratio (PAPR) reduction method for the wireless sensor networks (WSNs) is presented. The transmit power of wireless nodes in an ad hoc network is strictly limited. Thus, high PAPR of the 3D OFDM system is a possible drawback when it is considered as a physical layer transmission scheme for the WSNs. Here, we propose an improved partial transmit sequence (PTS) technique to reduce PAPR of the OFDM system with 3D modulation formats. In the proposed algorithm, the components of 3D signals are assigned to different subblocks using a diagonal rule (DR), increasing randomness of the signals in the disjoint subblocks forcibly. As a result, the proposed method reduces PAPR of the 3D OFDM system significantly without increase in computational complexity. Hence, the proposed algorithm makes the 3D OFDM system be a possible candidate for a physical layer transmission scheme in future WSNs.

SummaryIn wireless telecommunication, one of the modulation approaches used is the orthogonal frequency division multiplexing (OFDM). Moreover, the high peak‐to‐average power ratio (PAPR) is the one notorious demerit in OFDM systems. Hence, the high power amplifier (HPA) is used in its linear region. Otherwise, the bit error rate (BER) will be increased. Several approaches are proposed in the wireless communications for reducing the PAPR issue. In this paper, we propose a hybrid Discrete Hartley Matrix Transform (DHMT) precoding using both selected mapping (SLM) and partial transmit sequence (PTS) PAPR reduction strategies. For the multicarrier modulation process, instead of Inverse Fast Fourier transform (IFFT) operation, the DHMT operation is used because of its low computational complexity. Based on multi‐chaotic, the time‐frequency domain encryption (TFDE) approach is adopted for physical layer security to confirm the security in data transmission. For enhancing the physical layer security, the proposed encryption system generates chaotic sequences based on Logistic maps and Lozi in the frequency and time domains together. In this study, the implementation of the DHMT‐based OFDM system is processed to reduce the maximum PAPR. Implementation is performed on the MATLAB platform, and the performances are calculated using complementary cumulative distribution function (CCDF), BER regards to signal‐to‐noise ratio (SNR), and the outputs are compared based on the computation time. However, compared with the existing models, the proposed model produced better PAPR minimization regarding SNR.

The most widely used technique for high-data-rate transmission is orthogonal frequency division multiplexing (OFDM). However, one disadvantage of OFDM systems is that the transmitted signals have a high peak-to-average power ratio (PAPR). High PAPR causes more interference and lower resolution in analogue to digital (A/D) and digital to analogue (D/A) converters. In this paper, Partial Transmit Sequence (PTS) technique using Improved Harmony Search (IHS) algorithm is proposed to solve the high PAPR problem. The PTS technique has a high search complexity because it involves an extensive random search over all possible phase vector combinations, which grows exponentially with the number of phase vectors. IHS improves the accuracy and convergence rate of conventional algorithms while requiring only a few parameters to be adjusted. The modulation method used is Quadrature Phase Shift Keying (QPSK). The performance of PTS and IHS-PTS are analyzed using CCDF graphs with different values of subcarriers and iterations. The PAPR reduction percentage increases more with using IHS-PTS compared to PTS only. To conclude, implementing IHS together with PTS can improve computational complexity in PTS and helps to reduce PAPR values even better in OFDM system.KeywordsImproved Harmony Search (IHS)Orthogonal frequency division multiplexing (OFDM)Peak average power ratio (PAPR)Partial Transmit Sequence (PTS)

Orthogonal Frequency Division Multiplexing (OFDM) is one of the attractive data transmission technologies in recent years because of its high data processing rate and its capable to combat inter-symbol interference (ISI) that come from multiple paths fading. Also, OFDM is the standard of new generation wireless communication systems. However, the high Peak-to-Average Power Ratio(PAPR) can influence the system performance through significantly degrading its signal quality in the nonlinear channel. Researchers propose several PAPR reduction algorithms, such as Clipping, Partial Transmit Sequences (PTS), selective mapping (SLM). In this paper we propose a novel turbo scheme combining PTS with adaptive tone reservation (TR) to reduce PAPR in OFDM systems. Conducted simulations show that the performance of PAPR with TR-enhanced Turbo PTS are superior to pervious works.