Robotic Mobile System's Performance-Based MIMO-OFDM Technology

Recently, multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been shown feasible for underwater acoustic communications via effective algorithms to handle the channel time-variability. In this paper, we propose to use nonbinary low density parity check (LDPC) codes to address two other main issues in OFDM: (i) plain (or uncoded) OFDM has poor performance in fading channels, and (ii) OFDM transmission has high peak to average power ratio (PAPR). We develop new methods to construct nonbinary regular and irregular LDPC codes that achieve excellent performance, match well with the underlying modulation, and can be encoded in linear time and in a parallel fashion. Based on the fact that the generator matrix of LDPC codes has high density, we further show how to reduce the PAPR considerably with minimal overhead. Experimental results confirm the excellent performance of the proposed nonbinary LDPC codes in multicarrier underwater acoustic communications.

A new family of low density parity-check (LDPC) codes, called as invertible subset LDPC (IS-LDPC) codes, was proposed for peak-to-average power ratio (PAPR) reduction in OFDM systems recently. In this paper, we propose a PAPR reduction scheme for orthogonal frequency-division multiple access (OFDMA) systems based on IS-LDPC codes. The proposed scheme maps the invertible subsets of IS-LDPC codewords onto subcarriers to construct invertible symbol subsets. Then, the invertible symbol subsets are inverted independently for reducing the PAPR of downlink OFDMA systems. There is no need to transmit the side information by extra channels, which significantly reduces the system overhead and eases the system design. Simulation results show that the PAPR reduction scheme based on IS-LDPC codes produces remarkable PAPR reduction performance and good error correction performance in downlink OFDMA systems. Therefore, the proposed PAPR reduction scheme could be an efficient solution to reduce the PAPR of downlink OFDMA systems.

In this paper, a novel cyclic constellation mapping method (CCM) is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. By properly choosing the move parameter, this method can obtain a considerable PAPR performance. Moreover, in order to demodulate the signal correctly at the receiver side, a pilot-aided estimation method is also introduced. Simulation results show that the proposed method achieves a better PAPR and bit-error rate (BER) performance than the conventional partial transmit sequences (PTS) while maintaining low computational complexity.

A novel encryption scheme using chaotic Zadoff-Chu matrix transform (ZCMT) precoding is proposed to improve both of the data security and performances in orthogonal frequency-division multiplexing (OFDM) transmission, where the security is significantly enhanced with a huge key space of ∼10400 provided by hyper digital chaos. The chaotic ZCMT matrix is generated with the reconfigurable parameters and row permutation of ZCMT matrix, both of which are predetermined by a hyper digital chaos. The OFDM data encryption using the chaotic ZCMT precoding effectively reduces the peak-to-average power ratio (PAPR) and consequently improves the OFDM transmission performance, if compared with the traditional OFDM transmission. The significant PAPR reduction is numerically analysed via the autocorrelation and the complementary cumulative distribution function (CCDF).

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.

High peak to average power ratio (PAPR) is a serious drawback for orthogonal frequency division multiplexing (OFDM) system as it reduces the efficiency of high-power amplifiers commonly used in the transmitter and causes spectral spillage. OFDM transmissions are also sensitive to frequency selective fading channels which can severely attenuate certain parts of the signal making it much more vulnerable to additive noise. This paper proposes an effective precoding technique with the dual ability to both reduce PAPR and condition the OFDM signal against frequency selective fading channels. It will be demonstrated that by advisedly creating diversity among the subcarriers of one OFDM symbol, and exploiting it with a dirty- paper-coding (DPC) approach, excellent bit-error-rate (BER) performance is achieved without reducing transmission rate. Low PAPR factor can also be obtained through a proper selection of diversity matrix that distributes the power of each modulated symbol over the OFDM block. Simulation results show that the proposed technique has not only better BER performance than the ordinary channel inversion but also similar PAPR reduction ability to the selective mapping (SLM) technique.

The demand for high-speed mobile wireless communications is rapidly growing. Orthogonal Frequency Division Multiplexing (OFDM) technology promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for wireless communication systems of the near future. The practical results will be more yielding when the OFDM is combined with Radio Over Fiber technology (ROF). This project presents an investigation of the performance of OFDM-ROF system based on papers [95] [96] [97] [98] in terms of peak power reduction capability and degradation of channel capacity. OFDM is an attractive technique for achieving high-bit-rate wireless data transmission. However, the potentially large peak-to-average power ratio (PAPR) of a multicarrier signal has limited its application. The analysis is based on three sections 1. Peak to average power ratio 2. Signal distortion and channel capacity 3. ROF transmission. This report is organized as follows. After the introduction in the second chapter, OFDM and its principles are studied. Thirdly, is a throughput on the basic ROF technology. The fourth chapter is based onthe OFDM-ROF system, its basic model and description. Fifth chapter is PAPR and instantaneous power analysis. The effect of the envelope clipping on the peak-to-average power ratio (PAPR) and then instantaneous power of the band-limited OFDM signal is studied. While doing the PAPR analysis, the different approaches for the reduction of PAPR by different authors are compared. The sixth chapter is about the Signal distortion and channel capacity over additive white Gaussian noise and Rayleigh fading channels. The capacity calculations shown are based on the assumption that the distortion terms caused by the clipping are Gaussian. In the seventh chapter the ROF transmission performance is based on split-step Fourier method and nonlinear Schrödinger equation. The transmission performance is discussed from the measurement values by incorporating the spectral distribution of a modulation signal into the calculation of composite triple beats. The dynamic range of OFDM-64QAM which is evaluated from the calculations of Desired to Undesired Signal Ratio (DUR) is also presented. Thus, this project evaluates the OFDM-ROF system as a candidate for the future (4G) wireless system design.

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.

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.

Orthogonal frequency division multiplexing (OFDM) signals have a generic problem of high peak to average power ratio (PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. The drawback of the high PAPR is that the dynamic range of the power amplifiers (PA) & digital-to-analog (D/A) converters required during the transmission and reception of the signal is higher. As a result, the total cost of the transceiver increases, with reduced efficiency. This paper includes an idea of the PAPR constraint, along with the implementation and analysis of some specific algorithms for PAPR reduction of the OFDM signals. All the PAPR reduction algorithms are implemented and tested in the OFDM transceiver designed using Matlab. Analyzing some specific algorithms, we propose a novel algorithm by combining the subcarrier phase adjustment and linear combination of the time domain OFDM signals. Simulation results for a OFDM system employing Quadrature Amplitude Shift Keying (QASK) symbols and Quadrature Amplitude Modulation (QAM) can achieve a PAPR reduction of 5 dB.

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.

Orthogonal Frequency Division Multiplexing (OFDM) technology has high spectrum efficiency and good anti-multipath interference capacity, but it has an inherent shortcoming that high peak-average power ratio (PAPR). Select Mapping (SLM) method is an effective algorithm to reduce Peak to Average Power Ratio (PAPR) of OFDM (Orthogonal Frequency Division Multiplexing) signal, and does not bring about any distortion of the signal. However, the biggest disadvantage of SLM method is that computational complexity is very large. In this paper, we propose a kind of improved SLM scheme which combines superimposed training sequence method, which using the a pre-set threshold method to select sub-optimization phase sequence as the phase factor in the procession of SLM method on signals. The simulation results show that the proposed scheme can not only effectively reduce the PAPR of system, not only reduce the computational complexity of the system, at the same time, there is no significant effect on system performance.

High peak-to-average power ratio (PAPR) is still one of the major problems in orthogonal frequency division multiplexing (OFDM). In this article, a new precoding method is proposed and analyzed based on complex Vandermonde matrix (CVM). The reduction in PAPR of the OFDM signal is obtained using the decorrelation property of CVM which removes any redundancy from the input sequence and can be a very effective for PAPR reduction. Also, the phase-rotation property of CVM takes an advantage of the fact that the PAPR is very sensitive to phase-shifts of the signal. It is shown that the proposed precoding outperforms most of the powerful precoding techniques and can achieve a PAPR gain up to 6.5 and 7.4 dB for IEEE 802.11a and DVB-T OFDM systems respectively. Moreover, CVM precoding does not change power spectral levels or error performances when compared with the normal OFDM systems, also it does not increase the computational complexity when compared with the existing precoding methods. It is shown that the performance of the proposed precoding is independent of modulation schemes and the number of subcarriers. The proposed CVM precoding also takes advantage of the frequency variations of the communication channel and can provide considerable performance gain in fading-multipath channels.

Multicarrier modulation technique also known as Orthogonal Frequency Division Multiplexing (OFDM) is considered to be the most rapidly growing technique for 4th Generation wireless communication system. Due to its high speed data rate and its ability of multipath fading channel robustness. OFDM becomes an attractive technique and it is widely adopted in many wireless communications system. OFDM signal carries its major drawback of high Peak to Average Power Ratio (PAPR) problem. Out of band radiation and in band distortion produced due to its high PAPR. Mobile phone communication suffer severe drawback during its amplification. When OFDM employed a non linear Power Amplifier (PA), it produces the fluctuation in amplitude of OFDM signal. This paper discusses the method to overcome PAPR in terms of its performance by using improved clipping technique for PAPR reduction. This method is easy to implement and reduces the amount of PAPR by clipping the peak of the maximum power signal. We present an improved method for PARR reduction for reducing peak magnitude of OFDM signal. This scheme simultaneously minimizes the peak magnitude of PAPR in OFDM signal.

Visible light communication (VLC) is a technology that is currently being employed to achieve high data rates. Orthogonal frequency division multiplexing (OFDM) is a powerful scheme for intensity modulation and direct detection (IM-DD) that is becoming increasingly important. OFDM systems based on VLC are accomplished through the implementation of IM-DD constraints, including direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and asymmetrically clipped DC-biased (ADO-OFDM), among others. The OFDM technique based on VLC is inefficient in terms of spectral efficiency and has a high peak to average power ratio (PAPR). In this article, the symbol time compression-image adjust (STC-IMADJS) technique will be proposed for throughput maximization and PAPR reduction in the DCO-OFDM, ACO-OFDM, and ADO-OFDM systems. Furthermore, the STC technique enables the simultaneous transmission of two sub-carriers through Walsh spreading codes without inference between them. As a result, the OFDM symbol has been reduced by 50%. The IMADJS strategy reduces the high PAPR of transmitted signals by compressing large signals and expanding small signals, as long as the average power level remains constant after compression. Therefore, the proposed STC-IMADJS technique doubles the throughput as well as significantly reduces the PAPR for OFDM systems based on VLC. The simulation results are performed using Matlab-2021a for 1024 sub-carriers. As a result, the simulation results show that the proposed technique reduces the PAPR by 3.7 dB (86%), 8.16 dB (93%), and 1.81 dB (20%) for DCO-OFDM, ACO-OFDM, and ADO-OFDM systems respectively. Furthermore, the technique has a significantly lower computational complexity than conventional OFDM systems based on VLC. Finally, the measures of performance through this article are bit error rate and complementary cumulative distribution function.