A detailed Study of 4G in Wireless Communication: Looking insight in issues in OFDM : Looking insight in issues in OFDM

Description

As a promising technique, OFDM has been widely used in emerging broadband communication systems, such as digital audio broadcasting (DAB), high-definition television (HDTV), and wireless local area network (IEEE 802.11a and HIPERLAN/2). However, as the OFDM signals are the sum of signals with random amplitude and phase, they are likely to have large PAPR that require a linear high-power- amplifier (HPA) with an extremely high dynamic range which is expensive and inefficient. Furthermore, any amplifier nonlinearity causes intermodulation products resulting in unwanted out-of-band power. A number of approaches have been proposed to deal with the PAPR problem, including amongst others, clipping, clipping-and-filtering (CF), coding, companding transform, active constellation extension (ACE), selected mapping (SLM), and partial transmit sequence (PTS). This book proposes an improvement in the selected mapping technique. The resulting scheme can also be applied to the multiple transmitting antenna cases. Further, it compares the simulation results to the existing techniques namely exponential companding transform, repeated clipping and filtering, and adaptive active constellation extension. Auszug aus dem Text Text Sample: Chapter 2.1, Different methods for Peak-to-Average Power (PAPR) Reduction in Orthogonal Frequency Division Multiplexing (OFDM): Himanshu Bhushan Mishra et al.in 2012 proposed a new Selective-Mapping (SLM) technique in WIMAX without side information which is the major issue in the classical SLM Technique. In this paper the PAPR performance is measured using complementary cumulative distribution function (CCDF) plot and the probability of SI detection error performance have been evaluated as the criteria for WiMAX standard IEEE 802.16e. WiMAX with its standard IEEE 802.16d/e is the advanced technology used for long range communication with high data rate. It is well known that the Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for getting high data rates in a multipath fading environment. Hence, the physical layer of WiMAX uses OFDM. But the main disadvantage of OFDM is the high peak to average power ratio (PAPR). In this paper PAPR reduction is achieved using selected mapping (SLM) technique and simultaneously without sending the side information (SI) along with the OFDM symbol [1]. E. Al-Dalakta et al. in 2012 proposed an efficient technique for reducing the bit error rate (BER) of Orthogonal Frequency Division Multiplexing (OFDM) signals transmitted over nonlinear solid-state power amplifiers (SSPAs).The proposed technique is based on predicting the distortion power that an SSPA would generate due to the nonlinear characteristics of such devices. Similar to the Selective-Mapping (SLM) or Partial-Transmit-Sequence (PTS) schemes, the predicted distortion is used to select a set of phases that minimize the actual SSPA distortion. Simulation results confirmed that the signal-to-noise ratio that is required to obtain a BER of ∼〖10〗^ (-4) using the proposed technique is less by about 8 dB when it is compared to the standard PTS utilizing 16 partitions. Moreover, complexity analysis demonstrated that the proposed system offers a significant complexity reduction of about 60% compared to state-of-the-art methods. This work demonstrated that less direct PAPR indicators can provide better performance when combined with distortion less techniques such as PTS and SLM. Therefore, the proposed techniques are optimized to combat the consequences of high PAPR rather than reducing the PAPR itself. The proposed techniques are based on using the distortion level to select the optimal PTS and SLM system parameters [2]. Shiann-Shiun Jeng et al. in 2011 proposes a new method based on companding Peak-to-Average Power Ratio (PAPR) Reduction of Orthogonal Frequency Division Multiplexing (OFDM) signals. This paper suggests that uniformly distributed companding scheme and piecewise companding scheme cannot deliver the performance that satisfies various requirements of the system. So, the distribution of the OFDM signal is transformed into the trapezium distribution and the general formulas for the proposed scheme are derived that enable the de- sired performance to be achieved by controlling the parameter. The simulation results reveal that the proposed scheme may offer the more efficient PAPR reduction or the lower BER than the uniformly-distributed and piecewise schemes under the condition of efficient PAPR reduction or efficient BER performance [3]. Suma M N et al. gives a survey on developments in OFDM so far. He suggested that apart from high Peak-to-Average Power Ratio (PAPR) there are many more techniques that are needed to increase the performance of OFDM systems like interference cancellation, phase noise mitigation, Synchronization among carriers and post equalization. In today's communication scenario, high data rate single-carrier transmission may not be feasible due to too much complexity of the equalizer in the receiver. To overcome the frequency selectivity of the wide band channel experienced by single-carrier transmission, multiple carriers can be used for high rate data transmission. Orthogonal Frequency Division Multiplexing (OFDM), is multicarrier system which has become a modulation in physical layer of next generation WiMAX, LTE system. In this work effort is made to present challenges in OFDM and work done so far in channel equalization and different transforms used in OFDM system like Discrete Fourier Transform (DFT) Based OFDM, Discrete Cosine Transform (DCT) Based OFDM, Wavelet based and Wavelet packet based OFDM, Discrete Hartley Transform (DHT) Based OFDM, and Coded OFDM which includes Turbo codes and Alamouti codes [4]. Jun Hou et al. proposed a nonlinear companding scheme to reduce the Peak-to-Average Power Ratio (PAPR) and improve Bit Error Rate (BER) for OFDM systems. This proposed scheme mainly focuses on compressing the large signals, while maintaining the average power constant by properly choosing transform parameters. Moreover, analysis shows that the proposed scheme without decompanding at the receiver can also offer a good BER performance. Finally, simulation results show that the proposed scheme outperforms other companding scheme in terms of spectrum side-lobes, PAPR reduction and BER performance [5]. Yuan Jiang in 2010 suggest a new companding algorithm that offers improved performance in terms of BER and OBI while reducing PAPR effectively. Orthogonal Frequency Division Multiplexing (OFDM) mitigates the effect of inter symbol interference (ISI) but it suffers from inter-block interference (IBI).A good remedy for the OBI is companding. This paper proposes and evaluates a new companding algorithm. This work uses the special airy function and is able to offer an improved bit error rate (BER) and minimized OBI while reducing PAPR effectively [6]. Kitaek Bae et al. in 2010 proposed a new method for Peak-to-Average Power Ratio (PAPR) Reduction in Orthogonal Frequency Division Multiplexing (OFDM), a novel Active Constellation Extension (ACE) algorithm with adaptive clipping control namely Adaptive ACE which is an improvement in the technique based on the combination of two techniques namely clipping and Active Constellation Extension (ACE) known as Clipping-Based Active Constellation Extension (CB-ACE) technique. This work suggests that CB-ACE cannot achieve the minimum PAR when the target clipping level is set below an initially unknown optimum value. To overcome this low clipping ratio problem, Adaptive ACE is proposed. Simulation results demonstrate that proposed algorithm can reach the minimum PAR for severely low clipping ratios. In addition, the trade-off between PAR and the loss in E_b⁄N_o over an AWGN channel in terms of the clipping ratio has also been described [7]. Biographische Informationen Mrs Neelam Dewangan is an assistant professor at Chhatrapati /shivaji Institute of Technology, Durg. She has completed her M.Tech in communication engineering from the Chhatrapati /shivaji Institute of Technology, and under the supervision of Mr. Mangal Singh, the professor and head of the Institute. Moreover, she has published many papers and attended many conferences in her area of interest including wireless communication, 4G, LTE, and mobile communication.