Performance Analysis of SIMO–OFDM Systems With Pilot-Aided Channel Estimation

One possible solution to improve the utilization of the capacity of time-varying radio channels is to make the transceivers adaptive. Application of adaptive modulation in orthogonal frequency division multiplexing (OFDM) systems is of particular interest. The objective of this paper is to investigate the receiver algorithms capable of blindly recognizing the modulation format of the received signal in adaptive OFDM systems of the HiperLAN/2 type. The performance of the studied algorithms is considered by computer simulations in OFDM system with adaptive modulation and channel estimation. The maximum likelihood (ML) and the generalized likelihood ratio test (GLRT) classifiers require only few symbols to provide acceptable performance when good channel estimation and relatively high SNR values are available. The novel classifier requires high SNR and more symbols to achieve acceptable performance, but its computational complexity is still lower than that of the ML and the GLRT classifiers.

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.

In this paper, an integrated Orthogonal Frequency Division Multiplexing (OFDM) system is developed to improve Bit Error Rate (BER) performance of communication systems in order to meet the requirements of advanced communication systems like long term evaluation advanced (LTE –A). The proposed OFDM system consists of channel estimation using comb type pilot arrangement and convolution encoder with the best known Coding Bounds and Maximum A Posteriori (MAP) decoder. Using pilot symbols, the channel quality is estimated. The BER performance of OFDM system is improved using pilot carriers, channel estimation schemes and MAP decoder at the best known coding bounds. The system performance is analyzed with recursive systematic and non-systematic convolution codes, ML and MAP decoders. From the results, it is evident that the proposed OFDM system with channel estimation and MAP decoder at the best known coding bounds improves the system performance significantly.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

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.

The paper proposes a new iterative method to estimate the carrier frequency offset (CFO) with scattered pilot symbols inserted for channel estimation in orthogonal frequency division multiplexing (OFDM) systems. Assuming that the channel remains constant during a few consecutive OFDM blocks, the new method uses the correlations of the pilot symbols in these consecutive OFDM blocks. And an iterative concept is also employed to reduce the inter-carrier interference (ICI) that deteriorates the CFO estimation performance. After a few iterations, the proposed method can achieve the accuracy with no ICI. The mean square error (MSE) of the new method is analyzed and simulation results show the new method outperforms existing methods.

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.

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.

This paper presents the joint maximum likelihood (ML) time and frequency offset estimator exploiting antenna diversity in orthogonal frequency division multiplexing (OFDM) systems. Redundant information contained within the cyclic prefix (CP) is used and furthermore, we propose a new correlation coefficient for ML estimation and can obtain diversity gain from several received antenna signals. The method is efficient in an environment having a low signal to noise ratio (SNR) and multipath channel by combining the received signals from antennas in an OFDM system. In this paper we demonstrate an example of ML estimation from two received antenna signal.

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.

Adaptive coded modulation (ACM) is a key technique to increase spectral as well as power efficiency for orthogonal frequency division multiplexing (OFDM) systems. In this paper, an efficient rate adaptive low density parity check (LDPC) coded modulation (RALCM) algorithm is proposed, which maximizes the payload rate for OFDM systems under the constraint of the given transmit power and the target bit error rate (BER). Taking advantage of the two dimensional look up table for the signal to noise ratio (SNR) thresholds, the RALCM algorithm assigns different combinations of the LDPC code rates and quadrature amplitude modulation (QAM) modulations for subcarriers according to the channel frequency response (CFR). Both theoretical analysis and computer simulation show that the proposed algorithm not only efficiently improves the payload rate of the LDPC coded OFDM system over frequency selective fading channels, but also inherently reduces the computational complexity of the system optimization.

In this paper, we propose a transmission scheme to obtain a diversity gain in orthogonal frequency division multiplexing (OFDM) systems using spatial multiplexing (SM) transmission. In multiple- input multiple-output (MIMO) transmission, SM is advantageous for high-speed transmission when the signal to noise power ratio (SNR) is sufficiently high, whereas transmit diversity is preferable to SM when SNR is low. That is, there is a trade-off between high-speed transmission and reliable transmission. In this paper, we propose mutual superposition transmission (MST) in order to realize reliable SM-OFDM systems without reducing the transmission speed. In the proposed MST, two data symbols of two different subcarriers are mutually superposed on respective subcarriers after being weighted. Since each of superposed symbols contains two data symbols and is transmitted on each subcarrier, diversity can be achieved. As a result, the proposed method achieves a reliable SM transmission. We illustrate three types of MST and verify their effectiveness. From simulation results, we can show that the SM- OFDM system with the proposed MST of Type 1 achieves a better error rate performance than its original system conditioned on the same transmission rate.

Orthogonal Frequency Division Multiplexing (OFDM) system is used for the reducing almost every kind of interference in any communication system. For designing OFDM system need to use FFT and IDFT phenomena of signal processing, in this work mainly concern to improve peak to average power ratio for this system because this system is multicarrier system, and in the multiple carriers are nearly having same frequency but still they do not overlap to each other because these multiple carriers are orthogonal to each other. These multiple carriers have different power and energy levels so we get very unfair PAPR for this system here channel codes can be use to improve PAPR for that system, so in this work we will focus on the Comparing PAPR of OFDM system for different Channel codes.

Selective mapping (SLM) is an attractive method to reduce the peak-to-average power ratio (PAPR) without causing any signal distortion in orthogonal frequency division multiplexing (OFDM) systems. The main drawback of this technique is the requirement of sending side information (SI) to the receiver for each data block which results in huge bandwidth and power overheads. Also, it may degrade the bit error rate (BER) performance of the system due to the corruption of SI over the channel. In this paper, we propose a novel technique to reduce PAPR in single input single output and single input multiple output OFDM systems using Hadamard code-based SLM. The proposed method eliminates the need for explicit SI resulting in better bandwidth and power efficiency. The basic idea is to embed the SI of each data block within the data block itself at some specific locations using special multiplying sequences. Furthermore, the proposed scheme yields superior PAPR reduction when compared to that of the conventional SLM for an equivalent system complexity. Simulation studies show that the receiver achieves a better BER performance with the proposed technique as compared to the conventional SLM.

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.