Abstract— Emergent telecommunication systems use spectral efficient multilevel modulation formats together with multicarrier schemes such as Orthogonal Frequency division multiplexing (OFDM). OFDM transmission is an efficient way to deal with multipath. However one of its major drawbacks is its sensitivity to nonlinear distortions due to its greatly variable envelope and high peak to average power ratio (PAPR). Nonlinear distortions are mainly introduced by high power amplifiers (HPA), cause in band distortions. Misalignments in IQ modulators and demodulators causes imbalance, which results in loss of orthogonality and create intercarrier interference and spectral regrowth in an OFDM system. Nonlinear distortions also cause intermodulation effect. This degrades Bit error rate (BER) performance of the system. This paper introduces the self organization map(SOM) and parameterless self organization map(PLSOM) based and Hiperlan/2 receiver structure used for the compensation of nonlinear distortions. Simulation results presented in this paper clearly indicate the improved performance of the proposed system. Simulations are run for AWGN channel model and for two HPA models namely Travelling wave tube amplifier (TWTA) and Solid state power amplifier (SSPA), with and without SOM and PLSOM neural network blocks. Index Terms— OFDM; HPA; TWTA; SSPA; BER; AWGN; SOM; PLSOM I. INTRODUCTION Wireless LAN standards such as Hiperlan/2 and 802.11a use OFDM as a multi-carrier modulation/multiplexing technique. OFDM transmission exhibits many benefits in wireless communications. An OFDM signal is the sum of sinusoids transmitted through multicarriers, so that peak power of the OFDM signal increases in proportion to the number of subcarriers. In OFDM systems, the combination of different signals with different phase and frequency gives a large dynamic range that is used to be characterized by a high PAPR, which results in severe clipping effects and nonlinear distortion if the composite time signal is amplified by a power amplifier which have nonlinear transfer function. This degrades the performance of an OFDM system [1-3]. As a result, multicarrier systems are more sensitive to presence of nonlinearities. Due to large dynamic range of the modulated Manuscript received April 10, 2012; revised May 30, 2012. S. Rathkanthiwar is with Yeshwantrao Chavan College of Engineering, Nagpur, India, as an Associate Professor in Department of Electronics Engineering (e-mail: svr_1967@yahoo.com). C. Dethe is working as Principal, in Priyadarshini Institute of Enginnering and Technology, Nagpur, India. (e-mail: cgdethe@yahoo.com). K. Kulat is with Vishvesaraya National Institute of Technology, and is working as Professor and Head of Electronics Engineering Department. (e-mail: kishore_kulat@yahoo.com) signal, nonlinear distortion at the power amplifier causes interference both inside, resulting in intermodulation among the subcarriers as well as outside, which causes spectral spreading of OFDM signal. In band distortion may result in intermodulation, which is a mutual interference between signals spaced apart in frequency, after nonlinear amplification of signal by HPA. This causes degradation in Bit error rate (BER) performance of the system. Out of band components affect adjacent frequency band components [4]. A measure of the degradation can be very helpful in evaluating the performance of a given system, and in designing a signaling set that avoids degradation. This paper presents the performance of Hiperlan/2 with power amplifiers to study the effects of nonlinearities on the received signal. Back off strategies will then be used to minimize the effects of nonlinear distortions on the signal constellation of 16 QAM signal. TWTA and SSPA models are most commonly used power amplifiers in wireless communication systems. To achieve maximum output power efficiency, HPA is usually operated in the saturation region, which is basically a nonlinear region. As OFDM signal is characterized by high PAPR and large dynamic variation of the signal amplitude, it is highly affected by nonlinear distortion [5]. Basic Hiperlan/2 model to be simulated is shown in Figure 1 Fig. 1. Hiperlan/2 Model From fig. 1, first block is Bernauli binary generator block that provides the information source for the simulation. Convolutional code block creates convolutional code for the binary data. It encodes the sequence of binary input vectors to produce a sequence of binary output vectors. Puncture block carries out puncturing. It periodically removes bits from the encoded bit stream thereby increasing the code rate. Puncture pattern is specified by the puncture vector parameter in the mask. Matrix interleaver block permutes input symbols by filling a matrix by rows and emptying it by columns. General block interleaver block rearranges the elements of its input vector without repeating or omitting any elements. Rectangular QAM modulator base band block modulates using M ary QAM with a constellation on a rectangular A Neural Approach for Compensation of Effects of PAPR Causing BER Degradations in Hiperlan2 Shubhangi Rathkanthiwar, Chandrashekhar Dethe, and Kishore Kulat 365 International Journal of Modeling and Optimization, Vol. 2, No. 3, June 2012