Peak-to-average Power Ratio Characteristics Research Articles

DFT-Spread OTFS Communication System with the Reductions of PAPR and Nonlinear Degradation

The orthogonal time frequency space (OTFS) system with two-dimensional (2-D) modulation technique is an attractive technology to show the better performance than the conventional orthogonal frequency division multiplexing (OFDM) system, particularly in the high-speed vehicle communications and high-level dimensions of multiple-input multiple-output systems. However, the OTFS system has high peak-to-average power ratio (PAPR), like OFDM system. In this paper, we analyze the PAPR characteristics of the OTFS signal and propose a concept of discrete Fourier transform (DFT)-Spread OTFS system to reduce the PAPR efficiently. The key idea of the DFT precoding technique is to spread the energy of a subcarrier throughout the subcarriers. Therefore, the PAPR is decreased. In the practical wireless communication systems, the power efficiency could become worse, or the bit error rate (BER) is seriously degraded by the high peak signal power in a high power amplifier (HPA). So, by reducing the PAPR, the efficiency of the HPA can be significantly improved and the nonlinear distortion caused by HPA can be decreased, too. We evaluate the spectrum characteristics of conventional OFDM and OTFS schemes and the proposed DFT-Spread OTFS scheme according to the different nonlinear conditions of HPA. Simulation results demonstrate that the power spectrums of the proposed system are less sensitive than the conventional schemes in HPA nonlinear environments. In addition, we compare the uncoded BER performance among the different schemes over the AWGN and delay-Doppler channels according to the several HPA nonlinear conditions for the different mobility speeds of user equipment. The BER performance of the conventional OFDM system breaks down completely in high-mobility scenarios for both HPA linear and nonlinear conditions. The proposed scheme improves the BER performance over AWGN and delay-Doppler channels in HPA nonlinear environments, as compared to the conventional OTFS system. In high-mobility scenarios and at BER of $$1 \times 10^{ - 3}$$ , simulation results verify that the OTFS and our proposed scheme can achieve a gain of 12.8 dB compared to OFDM scheme. Moreover, the proposed DFT-Spread OTFS scheme can be reduced PAPR by 2.2 dB and 1.8 dB compared to OFDM and OTFS schemes, respectively.

Theoretical Analysis of the Peak-to-Average Power Ratio and Optimal Pulse Shaping Filter Design for GFDM Systems

Generalized frequency division multiplexing (GFDM) has been regarded as a candidate for new multicarrier modulation schemes in future wireless communication systems (e.g., 5G systems). However, GFDM systems still suffer from the problem of high peak-to-average power ratio (PAPR). In this paper, theoretical analysis of the PAPR distribution for GFDM signals is performed. Exact closed-form expressions for the complementary cumulative distribution function (CCDF) of PAPR are firstly derived for critically sampled and oversampled GFDM signals, respectively, which tend to be sufficiently accurate as the number of subcarriers K is large enough (e.g., K ≥ 64). With aid of theoretical analysis results, an optimization criterion for the design of pulse shaping filters is obtained, which can nearly achieve the globally minimum CCDF results and is appropriate for practical applications. This criterion can also achieve the globally optimal result for minimizing the variance of instantaneous power. Based on this criterion, a measurement for the overall deviation of filter coefficients is proposed, which can help to roughly and efficiently evaluate the ability of PAPR reduction for pulse shaping filters. Although the PAPR reduction effect is limited with pulse shaping filters, it is found that large deviation may also lead to higher PAPR. Additionally, with the aid of closed-form CCDF expressions, PAPR characteristics of GFDM and other multicarrier systems (e.g., OFDM and FBMC/OQAM) are compared thoroughly. Simulation results verify the validity and accuracy of derived theoretical results, and demonstrate the effectiveness of the proposed optimization design criterion.

4D-8PSK-TCM System for the Specrum and Power Efficient Satellite Communication

For the satellite communication, power efficiency and spectrum efficiency are all important requirements to keep the high speed data transmission and longer expectation of operation life of satellite. So, the Consultative Committee for Space Data Systems (CCSDS) has discussed many possible communication technology candidates and eventually has decided the 4D-8PSK-TCM (4 dimensional 8 phase shift keying trellis coded modulation) as one recommendation for X-band satellite communication system. Therefore, it is very important to propose the design structure of transmitter and receiver of the 4D-8PSK-TCM communication system and to evaluate the communication performances. In this paper, at first, the design method of 4D-8PSK-TCM system recommended in CCSDS for X-band satellite communication will be described in detail for the design of the transmitter and receiver. Secondly, the characteristics of peak to average power ratio (PAPR), spectrum characteristic, and constellation characteristic according to the square root raised cosine filtering are determined for each transmission efficiency mode. Finally, BER performances according to each reception processing step are evaluated and analyzed. As simulation results, the trajectory of the transmission signal according to the roll-off factor value and the PAPR characteristic and the spectral characteristic have been obtained. Acceptable PAPR characteristics have been obtained when the roll-off factor values are 0.35 and 0.5, and the spectral waveforms have been confirmed. Especially, it is confirmed that the receiver system using both the auxiliary trellis and the general trellis in the receiver is improved by 2 dB than the single auxiliary trellis system.

On the PTS Optimization Using the Firefly Algorithm for PAPR Reduction in OFDM Systems

ABSTRACTOrthogonal frequency division multiplexing (OFDM) is currently the most used technique for the high-data-rate transmission. However, OFDM systems have an inherent drawback in that the transmitted signals suffer from a high peak-to-average power ratio (PAPR). Partial transmit sequence (PTS) is generally applied to reduce the PAPR of an OFDM signal in wireless communication systems. Here, the search complexity for optimal phase vector increases exponentially with the number of phase vectors, since it involves an extensive random search over all the combinations of the allowed phase vectors. In this paper, a swarm intelligence algorithm for phase optimization based on the Firefly algorithm (FF) is applied to search the optimal combination of phase vectors. The proposed algorithm provides a superior trade-off between the improved PAPR performance and computational complexity when compared to the PTS scheme for a large number of sub-blocks. Simulation results show that the Firefly-algorithm-based PTS (FF-PTS) algorithm is an efficient method to achieve superior PAPR characteristics for OFDM signals when compared to conventional algorithms with very few parameters to adjust.

Filter bank SCFDMA: an efficient uplink strategy for future communication systems

This paper develops a generalized system model for the precoded multicarrier communication system, using basic multirate building blocks. Mathematical analysis of the proposed model is carried out, and the results are utilized in developing an efficient uplink wireless communication standard filter bank single carrier frequency division multiple access. The proposed system combines the low peak to average power ratio (PAPR) advantage of a single carrier communication system with the reduced out of band emission (OBE) of filter bank multicarrier (FBMC) scheme. The sensitivity of the proposed system to carrier frequency offset (CFO) is analyzed, and the results are utilized in developing a CFO compensation scheme with reduced complexity. A Nyquist filter design approach, which strikes a balance between OBE and tail size, is developed and is incorporated into the proposed system to enhance the OBE and PAPR characteristics. The instantaneous power of the proposed system is theoretically analyzed using characteristic function based approach, and the effectiveness of modifications is substantiated. A detailed simulation study is carried out to validate the performance of the proposals.

PAPR Constrained Power Allocation for Multicarrier Transmission in Multiuser SIMO Communications

Peak-to-average power ratio (PAPR) constrained power allocation for multicarrier transmission in multiuser single-input multiple-output (SIMO) communications is considered in this paper. Reducing the PAPR in any transmission system is beneficial because it allows the use of inexpensive energy-efficient power amplifiers. In this paper, we formulate a power allocation problem for single-carrier (SC) frequency division multiple access (FDMA) and orthogonal FDMA (OFDMA) transmission with instantaneous PAPR constraints. Moreover, a statistical approach is considered in which the power variance of the transmitted waveform is controlled. The constraints for the optimization problems are derived as a function of transmit power allocation and two successive convex approximations (SCAs) are derived for each of the constraints based on a change of variables (COV) and geometric programming (GP). In addition, the optimization problem is constrained by a user-specific quality of service (QoS) constraint. Hence, the proposed power allocation strategy jointly takes into account the channel quality and the PAPR characteristics of the power amplifier. The numerical results show that the proposed power allocation strategy can significantly improve the transmission efficiency of power-limited users. Therefore, it is especially beneficial for improving the performance for cell edge users.

SC-FDMA based systems to Reduce PAPR by using a Modified Companding Scheme

The 3rd generation partnership project (3GPP) long term evolution (LTE) standard uses single carrier frequency division multiple access (SCFDMA), scheme for the uplink transmissions and orthogonal frequency division multiplexing access (OFDMA) in downlink. SCFDMA makes use of single carrier modulation and frequency domain equalization, it is a technique that has similar performance and essentially the same overall complexity as those of OFDM, But in OFDMA high peak-to-average power ratio (PAPR) is a major drawback. An outstanding advantage of SC-FDMA is its lower PAPR due to its single carrier structure. In this paper, we analyze the PAPR of SC-FDMA signals with pulse shaping. We analytically derive the time domain SC-FDMA signals and numerically compare PAPR characteristics using the complementary cumulative distribution function (CCDF) of PAPR. The results show that SC-FDMA signals indeed have lower PAPR compared to those of OFDMA. Comparing the two forms of SC-FDMA, we find that localized FDMA (LFDMA) has higher PAPR than interleaved FDMA (IFDMA) but somewhat lower PAPR than OFDMA. Also noticeable is the fact that pulse shaping increases PAPR. To reduce the PAPR, we propose an efficient Kalman filter based PAPR reduction algorithm.

Improvement in the nonlinear tolerance for a DFT-spread CO-OFDM system using M-ASK modulation and Hermitian symmetry of a DFT

We propose a novel discrete Fourier transform (DFT) spread M-ary amplitude shift keying (M-ASK) coherent optical orthogonal frequency division multiplexing (CO-OFDM) with a Hermitian symmetry system to mitigate nonlinear effects by reducing the peak-to-average power ratio (PAPR) of the OFDM signals. The proposed DFT-spread M-ASK CO-OFDM with the Hermitian symmetry system has a lower PAPR than the conventional M2-quadrature amplitude modulation (QAM) CO-OFDM system using the DFT-spread scheme. Furthermore, to reduce the PAPR further as compared to the DFT-spread M2-QAM CO-OFDM system, the proposed system uses the Hermitian symmetry of the DFT, which enables the proposed system to have a lower modulation order of M instead of M2. The significantly reduced PAPR of the proposed system provides superior nonlinear tolerance. We analytically investigate the PAPR distributions of the OFDM systems. We also perform numerical simulations to investigate the PAPR characteristics and nonlinear tolerance of the OFDM systems. Our numerical results show that the proposed system outperforms the conventional CO-OFDM and DFT-spread CO-OFDM systems in terms of the bit error rate and PAPR.

Peak-to-Average Power Ratio Analysis for Golden Coded MIMO Systems

combination of the orthogonal frequency-division multiplexing (OFDM) technique and the multiple-input multiple-output (MIMO) architecture has emerged as a promising candidate for future wireless communications. The Space-time block coding (STBC) technique permits to fully take advantage of MIMO-OFDM systems and to effectively improve the channel capacity and the spatial diversity. The Golden Code (GC) is a full-rate and full-diversity, space-time code for 2 × 2 MIMO systems. Thanks to its algebraic construction, the GC achieves Diversity-Multiplexing gain trade-off and preserves the mutual information. However, it is well known that STBC-MIMO-OFDM systems are sensitive to the high Peak-to-Average-Power Ratio (PAPR) of the transmitted signals. The purpose of this paper is to analyze the PAPR of golden coded MIMO-OFDM systems. We investigate the effect of the roll-off factor on the PAPR characteristics and analyze the system performances. KeywordsOFDM, PAPR, Golden Code.

New OFDM structure with parallel combinatory code

We have introduced a flexible OFDM structure based on a promising property of IFFT operation. This structure can support uplink applications which include many transmitters using different numbers of subcarriers and one receiver with just one IFFT/FFT module with the subcarriers of the least common multiple (LCM) for the number of subcarriers of all the transmitters. In this paper, combining the parallel combinatory (PC) code and the proposed flexible OFDM structure, we report the design of a new OFDM system with PC code for various applications with a moderate transmission rate. The system can select appropriate phase sets for all modulated subcarriers for each PC code for different design requirements such as peak-to-average power ratio (PAPR) reduction or BER performance improvement. The proposed system will achieve better PAPR characteristics and promising BER performance. In addition, due to the flexible OFDM structure, the proposed PC-OFDM system will also have properties of high adaptability and compatibility.

PAPR Analysis of the OFDMA and SC-FDMA in the Uplink of a Mobile Communication System

In recent years, OFDMA(orthogonal frequency division multiple access) and SC-FDMA(Single Carrier Frequency Division Multiple Access) have been widely studied for the uplink of a mobile communication system. In this paper, PAPR(Peak-to-Average Power Ratio) and BER(Bit Error Rate) performance of the OFDMA and SC-FDMA systems are studied in relation to the uplink of a mobile communication system. Three kinds of sub-carrier allocation methods in the OFDMA system and 2 kinds of sub-carrier allocation methods in SC-FDMA system are suggested to compare and improve system performance. Simulation results show that in the OFDMA system, the first sub-band allocation method has better PAPR reduction performance than the other methods. In the SC-FDMA system, the distributed allocation method offers similar P APR, compared with the sub-band allocation method. P APR can be further reduced by adding a spectrum shaping filter with an appropriate roll of factor. Furthermore, it is found that on average, SC-FDMA can reduce the PAPR by more than 5 dB compared to OFDMA, when the total sub-carrier number is 1,024 and the sub-carrier number allocated to each user changes trom 8 to 512. Because of the frequency diversity and low PAPR characteristics, SC-FDMA system of the distributed sub-carrier allocation method can achieve better BER performance than the OFDMA system.