Peak-to-Average-Power-Ratio (PAPR) Reduction Techniques for Orthogonal-Frequency-Division- Multiplexing (OFDM) Transmission

Wireless communication has experienced an incredible growth in the last decade. Two decades ago,the number of mobile subscribers was less than 1% of the world\u27s population. As of 2011, the number of mobile subscribers has increased tremendously to 79.86% of the world\u27s population. Robust and high-rate data transmission in mobile environments faces severe problems due to the time-variant channel conditions, multipath fading and shadow fading. Fading is the main limitation on wireless communication channels. Frequency selective interference and fading, such as multipath fading, is a bandwidth bottleneck in the last mile which runs from the access point to the user. The last mile problem in wireless communication networks is caused by the environment of free space channels through which the signal propagates. Orthogonal Frequency Division Multiplexing (OFDM) is a promising modulation and multiplexing technique due to its robustness against multipath fading. Nevertheless, OFDM suffers from high Peak-to-Average- Power-Ratio (PAPR), which results in a complex OFDM signal. In this research, reduction of PAPR considering the out-of-band radiation and the regeneration of the time-domain signal peaks caused by filtering has been studied and is presented. Our PAPR reduction was 30% of the Discrete Fourier Transform (DFT) with Interleaved Frequency Division Multiple Access (IFDMA) utilizing Quadrature Phase Shift Keying (QPSK) and varying the roll-off factor. We show that pulse shaping does not affect the PAPR of Localized Frequency Division Multiple Access (LFDMA) as much as it affects the PAPR of IFDMA. Therefore, IFDMA has an important trade-off relationship between excess bandwidth and PAPR performance, since excess bandwidth increases as the roll-off factor increases. In addition, we studied a low complexity clipping scheme, applicable to IFDMA uplink and OFDM downlink systems for PAPR reduction. We show that the performance of the PAPR of the Interleaved-FDMA scheme is better than traditional OFDMA for the uplink transmission system. Our reduction of PAPR is 53% when IFDMA is used instead of OFDMA in the uplink direction. Furthermore, we also examined an important trade-off relationship between clipping distortion and quantization noise when the clipping scheme is used for OFDM downlink systems. Our results show a significant reduction in the PAPR and the out-of-band radiation caused by clipping for OFDM downlink transmission system

Performance Trade-off Investigation of B-IFDMA

A performance trade-off investigation is carried out between different possible uplink multiple access schemes, that are based on Orthogonal Frequency Division Multiplexing (OFDM), for International Mobile Telecommunication (IMT) Advanced systems. Between the Discrete Fourier Transform (DFT) precoded systems with different subcarrier allocation mappings and systems lacking DFT-precoders, Block Interleaved Frequency Division Multiple Access (B-IFDMA) is shown to provide a good trade-off between the frequency diversity collected, envelope properties achieved, and channel estimation performance compared to the other mapping schemes. The schemes are analyzed in the presence of the different possible modules which include equalizers, modulators, interleavers, and channel codes. In particular, robust codes such as Turbo codes are able to collect the diversity provided by such schemes, and B-IFDMA systems is shown to be able to beat the other systems in bit error rate (BER) performance terms

Frequency offset estimation for IFDMA uplink systems

This paper proposes two frequency offset estimation algorithms for the uplink of an Interleaved Frequency-Division Multiple-Access (IFDMA) system. One algorithm performs estimation in the frequency domain and the other in the time domain. Both algorithms are based on the maximum likelihood estimation (MLE) principle and use knowledge about pilot symbols. IFDMA utilizes a block-interleaved frequency allocation scheme to exploit the frequency diversity of the channel. In the presence of frequency offsets between users, multiple-access interference (MAI) appears, which has a negative impact on existing frequency offset estimation algorithms. The proposed algorithms are robust, since a special construction of pilot symbols allows to exclude a large amount of MAI in the presence of frequency offsets between users. As a result, the proposed time domain frequency estimation algorithm outperforms the frequency domain algorithm and all other known schemes

PAPR In LTE UPLINK : Problem and Improvement

LTE-Advanced is one of the most competing and widely adopted families of standards that will meet the 4G broadband wireless mobile communications requirements recommended by the IMT-Advanced for the terrestrial radio interface specifications. Pre-commercial deployments have proved that LTE-Advanced will ensure the competitiveness of the 4G mobile networks by providing a high-data-rate , low latency and optimized system. Unlike the IEEE802.16m WiMAX which uses OFDMA in both downlink and uplink multiple access schemes, LTE and its advanced version systems continue to use different multiple access transmissions in which OFDMA and SC-FDMA are supported in the downlink and the uplink, respectively. The idea to use OFDMA in the LTE uplink communications invoked discord among the members of the 3GPP standardization body because of the growing concern over the signal peakiness which degrades the efficiency of mobile station power battery consumption. The dire consequence of the peak amplitudes generated by the superposition of several subcarriers of identical phases led 3GPP to adopt SC-FDMA as an uplink multiple access method. Thus in this paper , the effect of pulse shaping on the performance of the uplink PAPR of distributed FDMA and localized FDMA will be dealt deeply. The performance improvement will be done by varying the roll-off factor of the raised-cosine filter for pulse shaping after IFFT.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Performance study of air interface for broadband wireless packet access

Ph.DDOCTOR OF PHILOSOPH

IMPLEMENTATION AND PERFORMANCE ANALYSIS OF LONG TERM EVOLUTION USING SOFTWARE DEFINED RADIO

The overwhelming changes in the field of communication brought about need for high data rates, which led to the development of a system known as Long Term Evolution (LTE). LTE made good use of Orthogonal Frequency Division Multiplexing Access (OFDMA) in its downlink and Single Carrier Frequency Division Multiplexing Access (SCFDMA) in its uplink transmission because of their robust performance. These multiple access techniques are the major focus of study in this thesis, with their implementation in the LTE system. GNU Radio is a software Defined Radio (SDR) platform. It comprises of C++ signal processing libraries. For user simplicity, it has graphical user interface (GUI) known as GNU Radio Companion (GRC), to build a signal processing flow graph. GRC translates any specific task flow graph to a python program which calls inbuiltC++ signal processing blocks. By leveraging this feature and existing modules in GRC, OFDMA and SCFDMA is implemented. In this study we made use of existing OFDMA flow graph of GNU Radio to study the behavior of downlink and general performing SCFDMA system was implemented with some modifications of the existing GNU Radio blocks. With the GNU Radio implementation, we tested the working mechanism of both the systems. OFDMA is used in downlink for achieving high spectral efficiency and SCFDMA was introduced in uplink due to its low PAPR feature. These multiple access schemes have to meet the requirement of high throughput with low BER and PAPR, low delays and low complexity. In this thesis we are focused on evaluating these multiple access techniques in terms of BER and PAPR with modulation techniques like QPSK, 16-QAM and 64-QAM. Performance analysis part is performed in MATLAB

Generalized Rake Receiver for Spreading-IFDMA Systems

Abstract. Spreading-Interleaved Frequency Division Multiple Access (IFDMA) providing code domain multiplexing for one IFDMA channel shows improved spectrum efficiency and good compatibility with CDMA systems while maintaining advantages of IFDMA systems. A generalized Rake receiver for Spreading-IFDMA is proposed in this paper, which combines jointly derepetition, equalization, and de-spreading processing. Similar to the conventional CDMA systems, the guard interval in Spreading-IFDMA symbols is not necessary, which means that spectrum efficiency can be further improved over IFDMA systems. With digital simulations and performance analysis, the proposed generalized Rake receiver demonstrates better BER performance, robustness, and lower computational complexity