Selected Mapping in Correlatively Coded OFDM

Orthogonal frequency division multiplexing (OFDM) has become an important component of waveform generation in wideband transmission. it's a superior technology for the high-speed rate of wired and wireless communication systems. Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM) systems are crucial wireless communication systems like 4G and 5G networks & tactical communication. The OFDM has many advantages over other techniques like its high capacity and immunity against multipath fading channels. However, one amongst the foremost drawbacks of the OFDM system is that the high-peak-to-average power ratio (PAPR) that leads the system to provide in-band distortion and out-of-band radiation and reduces its efficiency. This problem increases with a rise within the number of transmit antennas. Therefore, it's highly desirable to cut back the PAPR of an OFDM signal. For this, numerous techniques are proposed to beat the PAPR problem like i) Selective mapping (SLM) ii) Partial transmit sequence (PTS), iii) Clipping, iv) Clipping and filtering. All of those are reduced the PAPR by generating alternative subcarrier vector that are statistically independent OFDM symbols for a given data frame and transmitting the symbol with rock bottom peak power. During this paper we also proposed, some hybrid techniques. The hybrid techniques are the technique of clipping is employed in conjunction with SLM and PTS to cut back computational complexity. And also the combination of SLMPTS to scale back PAPR. Simulations are acquainted with analyze the efficiency of the techniques used which signifies OFDM to be providing much better PAPR reduction and a way better Bit Error Rate (BER). it's shown in simulation results that the proposed scheme performs well reducing PAPR. But the proposed scheme is more complex than the prevailing techniques.

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

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.

Based on superposition of signals in the time domain, we propose a new low-complexity scheme for the reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme first generates signal candidates by combining an OFDM signal and its cyclically delayed versions with different delays and phases, and then selects the candidate signal with minimum PAPR. It is shown that the complexity of the proposed scheme is significantly lower than that of the selective mapping (SLM) at the cost of some degradation in the bit error rate (BER) performance and, at similar PAPR and coded BER performance, is lower than that of the low-complexity SLM proposed recently.

High Peak to Average Power Ratio (PAPR) in the transmitted signal is still a very important challenge in Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we present a new Zadoff-Chu matrix Transform (ZCT) precoded Selected Mapping (SLM) based OFDM (SLM-OFDM) system for PAPR reduction. The proposed system is based on precoding the constellation symbols with ZCT precoder after the multiplication of phase rotation factor and before the Inverse Fast Fourier Transform (IFFT) in SLM-OFDM Systems. At the clipping probability of 10−3, simulation results show that our proposed system can reduce the PAPR up to 5.0 dB with N=64 (System subcarriers) and V=16 (Dissimilar phase sequences) for QPSK modulation. Additionally, ZCT based SLM-OFDM systems also take advantage of frequency variations of the communication channel and can also offer substantial performance gain in fading multipath channels.

Selected mapping (SLM) is an effective method for addressing high peak-to-average power ratio (PAPR) issues in orthogonal frequency division multiplexing (OFDM) systems. However, the standard SLM approach introduces additional data decoding challenges in the form of side information (SI) transmission and estimation. In general, SI transmission reduces data throughput and SI estimation normally involves computationally complex procedures, which increase design costs. To eliminate the need for both SI transmission and SI estimation, this paper presents an investigation into the PAPR reduction and BER performance of a new technique based on a modified SLM approach. It is shown that the proposed method simplifies data decoding through SI cancellation without SI transmission. Results show that the proposed method produces similar PAPR reduction performance and BER performance as standard SLM based OFDM system, which presumes perfect SI estimation, within a frequency non-selective (flat) fading channel.

Orthogonal frequency division multiplexing (OFDM) system has high spectral efficiency and immunity to frequency selective fading channel. So, it has been widely used in modern wireless communication systems. However, the major drawback of OFDM system is the high peak-to-average power ratio (PAPR) of the transmitted signal for large number of subcarriers. Selected mapping (SLM) is one of the most well-known technique to reduce the PAPR in OFDM system, since it can achieve a good PAPR reduction without signal distortion. Moreover, SLM technique can be used with wavelet-OFDM (WOFDM) system to enhance the PAPR performance, while maintaining most of the advantages of the conventional OFDM system. In this paper, an effective PAPR reduction technique using SLM-WOFDM based on particle swarm optimization (PSO) algorithm is proposed. PSO is applied to SLM-OFDM and SLM-WOFDM systems for searching the optimum phase rotation factors. The systems evaluation shows that the proposed PSO based SLM-WOFDM system provides better PAPR reduction compared to PSO based SLM-OFDM, SLM-WOFDM, and conventional SLM-OFDM systems.

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) systems suffer from high sidelobes level. In some applications, as cognitive radios, this phenomenon can be a serious matter. This paper proposes Minimum shift keying (MSK)-OFDM to address this problem. The proposed method is an OFDM system using MSK modulation in each subcarrier. The corresponding transmitter and receiver are introduced. The method doesn't entail great changes in the main parts of OFDM. Like OFDM systems, the transceiver can be implemented using DFT/IDFT. Simulation results show great reduction in out of band radiation in comparison with conventional OFDM.

It is well known that Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from intercarrier interference (ICI) in mobile environment due to loss of orthogonality among subcarriers caused by Doppler shifts. There exist many ICI mitigation techniques in the literature to improve the performance of OFDM systems. However, most of the existing ICI mitigation techniques assume the OFDM transmission bandwidth is narrow enough that the frequency offsets on all subcarriers are identical. In a wideband OFDM transmission or a non-contiguous OFDM spanning over large bandwidth, the Doppler shifts on different subcarriers are different, especially in high speed aerial vehicle communication systems. In this paper, we analyze the wideband OFDM system in high mobility environment where the frequency offsets vary from subcarrier to subcarrier. We then propose a novel ICI cancellation scheme to eliminate the ICI effect and offer the wideband OFDM system significantly improved BER performance. Simulation results in AWGN channel and multipath fading channel confirm the effectiveness of the proposed scheme in the presence of frequency offset and time variations in the channel, offering the best BER performance available which matches the BER performance of wideband OFDM system without ICI. To our knowledge, this paper is the first to address the ICI problem of varying frequency offsets across subcarriers in wideband OFDM system.

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.

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

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.

OFDM is a multicarrier modulation technique which is used in communication systems like Wireless Personal Area Network (WPAN), Wireless Local Area Network (WLAN), Wireless Metropolitan Area Network (WMAN), Wi-Max, DVB-T etc for the high rate transmission over wireless radio channels. It is commonly known as a transmission technique of high spectral efficiency and robustness against frequency selective fading. The advantages of OFDM include simple digital realization, compatibility with multipath fading channel, less complex receivers and improve the bandwidth efficiency. At the same time, it also increases system capacity providing reliable transmission. But the main problem of OFDM systems is Peak to average power ratio due to its envelope fluctuation. The objective of this project this to provide a broader understanding in peak-to-average power ratio (PAPR) problem in orthogonal frequency division multiplexing (OFDM) systems. This paper showcases main three reduction techniques, precoding and SLM in combination with nonlinear companding in detail considering advantages and disadvantages of each technique.

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.