REDUCTION OF PAPR IN MIMO-OFDM USING ADAPTIVE SLM AND PTS TECHNIQUE

Author Name: CH. Nagaraju , Anil Kumar Sharma , M.V. Subramanyam
Author Email: ch_nag2000@yahoo.com

Abstract

This work will focus on performance comparison between two methods for combating the effects of PAPR: i.e. Selective Mapping (SLM) and Partial Transmit Sequence (PTS) method. These two methods are compared in terms of bandwidth efficiency and computation complexity with BER and PAPR reduction performance. This paper also describes the analysis and simulation of a modified SLM and PTS approach to decrease PAPR in MIMO-OFDM system. The basic principle of the coding technique known as STBC-OFDM is demonstrated through derivations and simulations. BER- analysis of MIMO-OFDM system using space-time block codes are simulated for Alamouti 2×1   system. The performance of the proposed system is better in terms of SNR as compared to systems with lower antenna configurations. In this work, the conjugate symbols were proposed, which have the same PA property. The proposed algorithm shows better PAPR performance and complexity reduction than the usual algorithms using the simulation results obtained.

Introduction

Life without a proper communication has become an intricate these days. Even a common man who doesn’t have any knowledge of Communications enquires about the best communication service provider without any delays and thus leading to high data rate services. These services are always affected by various factors throughout the communication process, but so many novel approaches gave been established now and then in order to fulfil the requirements of users. Nowadays for high data rate services MIMO-OFDM system is well thought-out as one of the most exceptional methods. Mainly in wireless communications this system has hold its place firmly because of its advantages. Prior to this system a generic OFDM system is being explored for high speed data applications as OFDM offers power proficient signalling for a large number of subscribers on the same channel. MIMO-OFDM is used for numerous applications because of its high spectrum

efficiency and the resistance to inter-symbol interference (ISI). PAPR issue is innate in MIMO-OFDM system as it is developed in accordance with OFDM. The issue of PAPR is mainly dealt with a common problem in Communications i.e. signal distortion due to presence of independently modulated subcarriers and there arises a problem of Bit error rate (BER) [1]-[5].  In order to resolve BER an acquaintance of how different bit sequences are mapped. These days a number of modern sophisticated methods have been proposed in literature to reduce PAPR of OFDM Systems with a lot of ease [6]-[10]. Clipping is the easy and extensively used method to limit the PAPR below a threshold level; however it results in distortion and radiation (in-band and out-of-band). Another distinguished method to minimize PAPR is Block coding (the encoding of an input data into a codeword with low PAPR); consequently a decrease in data rate takes place. In this work an adaptive approach using selected mapping (SLM) and Partial transmit sequence (PTS) methods is proposed to minimize the PAPR without any signal distortion even though there is a chance of small increase in redundancy. Application of existing methods on each antenna is a clear-cut approach for reducing PAPR. Even though this approach is helpful for PAPR reduction without any difficulty, high complexity and large amount of side information (SI) are required [11]. Subsequently to solve this issue a contemporaneous algorithm is investigated, which selects the transmitted sequence with the minimum average (minaverage) PAPR over all transmit antennas. It lessens SI at the cost of a minor degradation of the PAPR performance. Nevertheless, the contemporaneous algorithm still requires numerous IFFT operations, which show high computational complexity. Here, a research on the property of space-time block coded (STBC) MIMO-OFDM systems is carried out extensively. For unfussiness, a STBC MIMO-OFDM system that make use of Alamouti scheme was considered, and it is established that the conjugate symbols transmitted on two antennas have same property. As a result, novel contemporaneous algorithms with low complexity were proposed, which require only half of IFFT operations for usual contemporaneous algorithms. Furthermore, a new standard of minimum maximum (minmax) was proposed, in order to achieve better PAPR performance than the standard of minaverage in usual contemporaneous algorithms. And hence the work proposed in this paper may also be applicable to systems with multiple transmit antennas. The simulation results shown in this work are depicted in the form of graphical representations and tabular columns have been framed wherever necessary to show the comparative analysis based on various attributes. The paper has been noticeably organized in a chronological order of methods and results as various sections for an easy perception of the research work.

Conclusion

In this work, we consider phase factor sequence mapping with conjugate symbols and we prove that the symbols have the similar PA property. With this property, the computation complexity of proposed modified concurrent algorithms is reduced to half. The concept of PAPR in OFDM signals and PAPR reduction techniques like SLM and PTS have been investigated. The investigation has been proved in a right way using the plots obtained after simulation process. This paper also described modified SLM and PTS approach to reduce PAPR in MIMO-OFDM systems under Rayleigh fading channels. The basic principle of MIMO STBC-OFDM coding technique based on ‘space and time’ is demonstrated through derivations and simulations. BER- analysis of MIMO-OFDM system using space-time block codes are simulated for Alamouti 2×1   system. The performance of the proposed system is better in terms of SNR as compared to systems with lower antenna configurations and this is shown in the paper with the help of a tabular column drawn for SNR values. In this work, the conjugate symbols were proposed, which have the same PA property. The proposed algorithm shows better PAPR performance and complexity reduction than the conventional algorithms.

References

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