OFDMA/SC-FDMA aided space-time shift keying for dispersive multi-user scenarios

Motivated by the recent concept of Space-Time Shift Keying (STSK) developed for achieving a flexible diversity versus multiplexing gain trade-off, we propose a novel Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier Frequency Division Multiple Access (SC-FDMA) aided multi-user STSK scheme for frequency-selective channels. The proposed OFDMA/SC-FDMA STSK scheme is capable of providing an improved performance in dispersive channels, while supporting multiple users in a multiple antenna aided wireless system. Furthermore, the scheme has the inherent potential of benefitting from the low-complexity single-stream Maximum-likelihood (ML) detector. Both an uncoded and a sophisticated near-capacity coded OFDMA/SC-FDMA STSK scheme were studied and their performances were compared in multiuser wideband Multiple-Input Multiple-Output (MIMO) scenarios. Explicitly, OFDMA/SC-FDMA aided STSK exhibits an excellent performance even in the presence of channel impairments due to the frequency-selectivity of wideband channels and proves to be a beneficial choice for high capacity multi-user MIMO systems

SC-FDM-IDMA Scheme Employing BCH Coding

In OFDM-IDMA scheme, intersymbol interference (ISI) is resolved by the OFDM layer and multiple access interference (MAI) is suppressed by the IDMA layer at low cost . However OFDM-IDMA scheme suffers high peak-to-average power ratio (PAPR) problem. For removing high PAPR problem a hybrid multiple access scheme SC-FDM-IDMA has been proposed. In this paper, bit error rate (BER) performance comparison of SC-FDM-IDMA scheme, OFDM-IDMA scheme and IDMA scheme have been duly presented.  Moreover, the BER performance of various subcarrier mapping methods for SC-FDM-IDMA scheme as well as other results with variation of different parameters have also been demonstrated. Finally simulation result for BER performance improvement has been shown employing BCH code. All the simulation results demonstrate the suitability of SC-FDM-IDMA scheme for wireless communication under AWGN channel environment

Performance study of air interface for broadband wireless packet access

Ph.DDOCTOR OF PHILOSOPH

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

Multicarrier modulation with variable peak‐to‐average power ratio using partial fast Fourier transform

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166180/1/cmu2bf01398.pd

PERFORMANCE EVALUATION OF A MULTICARRIER MIMO SYSTEM BASED ON DFT-PRECODING AND SUBCARRIER MAPPING

The ever-increasing end user demands are instigating the development of innovative methods targeting not only data rate enhancement but additionally better service quality in each subsequent wireless communication standard. This quest to achieve higher data rates has compelled the next generation communication technologies to use multicarrier systems e.g. orthogonal frequency division multiplexing (OFDM), while also relying on the multiple-input multiple-output (MIMO) technology. This paper is focused on implementing a MIMO-OFDM system and on using various techniques to optimize it in terms of the bit-error rate performance. The test case considered is a system implementation constituting the enabling technologies for 4G and beyond communication systems. The bit-error rate optimizations considered are based on preceding the OFDM modulation step by Discrete Fourier Transform (DFT) while also considering various subcarrier mapping schemes. MATLAB-based simulation of a 2 × 2 MIMO-OFDM system exhibits a maximum of 2 to 5 orders of magnitude reduction in bit-error rate due to DFT-precoding and subcarrier mapping respectively at high signal-to-noise ratio values in various environments. A 2-3dBs reduction in peak-to-average power ratio due to DFT-precoding in different environments is also exhibited in the various simulations

DFT spread-optical pulse amplitude modulation for visible light communication systems

DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) has been proposed in visible light communication (VLC) to overcome the limited modulation bandwidth of light emitting diode (LED). Due to the implementation of the inverse fast Fourier transform at the DCO-OFDM transmitter, DCO-OFDM suffers from its high peak-to-average power ratio (PAPR), which restricts its use in some VLC applications, especially where the optical power efficiency is a crucial requirement. That is because the LEDs used in VLC systems have a limited optical power-current linear range. To this end, a novel discrete Fourier transform spread-optical pulse amplitude modulation (DFTS-OPAM) signal scheme based on the single carrier-interleaved frequency division multiple access (SC-IFDMA) signal is introduced in this paper to address the high PAPR issue of OFDM. DFTS-OPAM is achieved by considering a PAM as an SC-IFDMA data symbol and duplicate the output vector of the fast Fourier transform at the SC-IFDMA transmitter side. Simulation results show that the PAPR of the proposed scheme is 7 dB lower than that of DCO-OFDM. Furthermore, this significant PAPR improvement is experimentally investigated where the practical results show that the proposed scheme can provide more 2.5 dB reduction in the average transmitted power requirement compared to DCO-OFDM and can subsequently increase the maximum achieved distance between the transmitter and the receiver up to 44%