Modulated OFDM Systems Research Articles

FPGA Implementation of a Phase Optimizer-Assisted PTS Scheme for PAPR Reduction in OFDM Systems

This article proposes a phase optimizer-assisted partial transmit sequence (PO-PTS) for minimizing PAPR values in OFDM systems. The novel PO-PTS scheme after validation, based on simulation results, is implemented using a Xilinx system generator on a field programmable gate array (FPGA). The phase optimizer (PO) module is employed to select optimal phase weighting factors to perform scaling with the data sequence in the PTS scheme. The computational complexity and the redundancy involved in producing the candidate signals are significantly reduced by the PO-PTS compared with the conventional PTS method. The proposed method reduces PAPR for a QPSK-OFDM signal by 56.16% compared to the original OFDM signal without compromising on the bit error rate (BER) performance. In addition, the performance of PO-PTS in terms of PAPR reduction for 32-QAM and 64-QAM modulated OFDM systems is also presented to justify the robustness of the proposed scheme. Moreover, when PO-PTS is implemented using FPGA, it uses only 1% of the hardware available in Virtex.

A use-case efficient DFrFT-based index modulated-OFDM system in the presence of CFO

Index modulated orthogonal frequency division multiplexing (OFDM-IM) only utilizes partial resources to transmit signals according to use case requirement, it leads to higher energy efficiency and spectral efficiency than the classical OFDM. However, in the presence of inter-carrier interference (ICI) due to carrier frequency offset (CFO), the performance of index modulated OFDM system severely deteriorates. To mitigate this issue, a novel discrete fractional Fourier transform (DFrFT) based OFDM-IM scheme over Rayleigh frequency selective fading channel is proposed in this paper. The optimum DFrFT angle (αopt) for this new scheme at various CFO values has been calculated theoretically. Incorporating these estimated αopt, the proposed system achieves a gain of 8 dB over conventional FFT-based OFDM-IM at bit error rate (BER) = 10−3 in a high normalized CFO (ϵ) environment (ϵ=0.2). The system model is also verified for different user applications, i.e., high data rate and low data rate applications. Simulation and analytical results show that the proposed model has a robust and superior performance compared to the conventional FFT-based OFDM-IM, DFrFT-based OFDM, and classical OFDM. Moreover, the proposed DFrFT-OFDM-IM model achieves all these superiorities with the same complexity as the conventional FFT-based OFDM-IM system.

Index Modulation OFDM Systems with Direct Pattern of Subcarrier Activation

OFDM-IM is a spatial modulation technique applied to OFDM's block subcarriers, resulting in a modified version of OFDM. Compared to traditional OFDM, OFDM-IM boasts several benefits, such as enhanced bit-error rate (BER) performance and power efficiency. When working with OFDM-IM, the specification of subcarrier-activation-patterns (SAPs) is done by utilizing either look-up tables (LUTs) or a combinatorial approach to conform with data. However, the data-to-SAP mapping methods of both suffer from increased complexity as the number of subcarriers expands. The paper proposes a direct data-to-SAP mapping that eliminates the need for any type of look-up tables. Through the presented analysis and computer simulation results, it is demonstrated that the OFDM-IM system utilizing the proposed mapping scheme outperforms equivalent traditional OFDM-IM systems in both complexity and bit error rate (BER) performance.

Pilot-based channel estimation in spatial modulated OFDM systems for mobile wireless applications

Spatial modulation Orthogonal Frequency Division Multiplexing (SM OFDM) is a newly developed transmission technique that has been proposed as an alternative for multiple input multiple output (MIMO)-OFDM transmission. Channel estimation is important for coherent data detection in practical scenarios. This paper investigates estimate power, Mean Square Error (MSE) and Bit Error Rate (BER) parameter metrics with channel estimation algorithm for Additive White Gaussian Noise (AWGN) and Rayleigh fading channel on three test environments proposed by International Telecommunication Union (ITU) specified standard model. Simulation output shows that for an AWGN channel, an improvement of approximately 1 dB and 0.3 dB power is obtained with Minimum Mean Square Error (MMSE) estimate and Least Square (LS)-linear/Spline using DFT. Additionally, for various interpolations employed, MSE decreases as Signal to Noise Ratio (SNR) rises, and performance improvement in BER when compared to traditional LS/MMSE estimators also occurs. For Rayleigh fading channel also there arises an enhanced performance in the parameter metrics with MMSE-DFT compared to conventional estimators. In summary, simulation output shows that incorporating DFT algorithm can provide better estimate power, BER and MSE by eliminating the effect of noise externally the extreme channel delay length.

Pilot-based channel estimation in spatial modulated OFDM systems for mobile wireless applications

Pilot-based channel estimation in spatial modulated OFDM systems for mobile wireless applications

Pilot Based MMSE Channel Estimation for Spatial Modulated OFDM Systems

Pilot Based MMSE Channel Estimation for Spatial Modulated OFDM Systems

An Efficient Hierarchical Modulation based Orthogonal Frequency Division Multiplexing Transmission Scheme for Digital Video Broadcasting

Due to the increase of users the efficient usage of spectrum plays an important role in digital terrestrial television networks. In digital video broadcasting, local and global content are transmitted by single frequency network and multifrequency network respectively. Multifrequency network support transmission of global content and it consumes large spectrum. Similarly local content are well supported by single frequency network. In order to provide better spectral efficiency both local and global contents are transmitted in single constellation using hierarchical modulation. Hierarchical modulated OFDM system provides good spectral efficiency and robustness to the fading environment. In this paper a hierarchical modulated OFDM system for local service insertion is analyzed and its performance under various channels is been discussed. Convolutional encoder is used in this paper.

Efficient Detection of Spatial Modulation OFDM Systems With Multiple Carrier Frequency Offsets

In this letter, an efficient detection scheme is proposed to mitigate the effect of the carrier frequency offset (CFO) in spatial modulation orthogonal frequency division multiplexing (SM-OFDM) systems. Specifically, the proposed scheme employs a novel symbol-by-symbol-aided iterative detector to the SM-OFDM systems with multiple CFOs, where the zero symbols are considered as constellation points. Simulation results demonstrate that the proposed scheme is capable of effectively mitigating the effect of multiple CFOs and of providing about considerable system performance improvement compared with the conventional parallel interference cancellation-aided maximum likelihood detector at a moderate complexity cost.

MSE expression for transform‐based decision‐directed channel estimation schemes in M‐PSK OFDM systems

An analytic mean squared error formula is derived for transform-based decision-directed channel estimation schemes in general M-ary phase shift keying modulated OFDM systems.

Optimal 16-Ary APSK Encoded Coherent Optical OFDM for Long-Haul Transmission

In this letter, an optimal 4+12 amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system is proposed (the numbers 4 and 12 represent the constellation points located in the inner ring and the outer ring, respectively). Although the 4+12APSK modulation format has smaller average Euclidean distance than 16 quadrature amplitude modulation (QAM), the 4+12APSK modulated CO-OFDM system has the best transmission performance, with increased tolerance towards both amplified spontaneous emission noise and fiber nonlinearities compared with 16QAM and 8+8APSK modulated OFDM systems. The maximum reach at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor=8.2 dB (when bit-error rate (BER) equals 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) is evaluated to assess the system performance based on a single-channel and five-channel wavelength division multiplexing (WDM) CO-OFDM system, and illustrates that the transmission performance of 4+12APSK modulated OFDM outperforms 8+8APSK modulated OFDM and 16QAM modulated OFDM by approximately 10.5%, and in the WDM system, it surpasses 8+8APSK modulated OFDM by approximately 5.6% and 16QAM modulated OFDM by 18.75%.

Adaptive Modulation Using Neuro-Fuzzy (N-F) Controller for OFDM System

As demand for high quality transmission increases, improving spectrum efficiency and error performance in wireless communication systems are important. OFDM is a multi-carrier modulation technique with densely spaced sub-carriers that has gained a lot of popularity among the broadband community in the last few years. One of the promising approaches to next generation communication systems are adaptive OFDM (AOFDM). Fixed modulation systems uses only one type of modulation scheme (or order), so that either performance or capacity should be compromised but in adaptive modulated systems change modulation scheme (or order) depending on instantaneous Signal to Noise Ratio (SNR) to attain superior performance and capacity compared to fixed modulated systems. Neuro-fuzzy controller combines advantages of fuzzy logic and neural networks. Neuro-fuzzy controller provides automatic adaption procedure to fuzzy logic controller. Neural networks requires sufficient prior knowledge to be initialized but neuro-fuzzy systems doesn't requires any prior knowledge to be initialized and is efficient compared to fuzzy logic and neural networks. In this paper we propose an adaptive modulated OFDM system using neuro-fuzzy controller. The proposed system is simulated in MATLAB and compared with existing systems, simulation results shown significant improvement in systems performance.  Index Terms—Adaptive modulation, OFDM, Neuro-Fuzzy controller

Erratum: Exact Error Performance Analysis of Arbitrary 2-D Modulation OFDM Systems with Carrier Frequency Offset [IEICE Transactions on Communications E95.B (2012) , No. 4 pp.1439-1442

Erratum: Exact Error Performance Analysis of Arbitrary 2-D Modulation OFDM Systems with Carrier Frequency Offset [IEICE Transactions on Communications E95.B (2012) , No. 4 pp.1439-1442

Exact Error Probability Analysis of Arbitrary 2-D Modulation-OFDM Systems with I/Q Imbalances

In OFDM systems, in-phase and quadrature (I/Q) imbalances generated in the analog front-end introduce inter-channel interference and, consequently, error performance degradation. This letter provides an exact expression involving the two-dimensional (2-D) Gaussian Q-function for the error probability of an arbitrary 2-D modulated OFDM signal with I/Q imbalances. The effects of I/Q imbalances on the distribution of an AWGN and the error performance are analyzed.

Performance of OFDM-Based Dual-Hop Amplify-and-Forward Relaying

In this letter, the end-to-end BER performance of a dual-hop OFDM-based relay system is investigated. The relay terminal operates in the amplify-and-forward (AF) mode. We derive the bit error rate (BER) of AF relaying with average power scaling (APS) constraint valid for source-relay link high signal- to-noise ratio conditions. We also study a frequency diversity technique that improves the performance of single antenna AF-APS relaying. The theoretical BER expressions are verified by computer simulations for a 4-QAM modulated OFDM system.

Variable LDPC coding rate performances for multicarrier systems using HD decoding

An adaptive coding scheme minimising the BER of a bit-interleaved coded modulation OFDM system performing hard-decisions (HD) after the demodulation and ideal interleaving is proposed. The subcarrier code rate levels subject to a rate constraint are varied according to perfect channel state information at the transmitter. The derived adaptive scheme uses low-density parity-check codes. A modified bit-flipping algorithm provides HD decoding and can be applied either alone or combined with a power loading scheme. It is shown by Monte Carlo simulations that, for broadband systems with Rayleigh fading, the loading procedure provides a signal-to-noise ratio gain up to 3dB for an average BER level of 10−5.

Pilot symbol assisted high speed packet transmission system based on adaptive OFDM in broadband mobile channel

4G mobile communication system requires the throughput of 10–100Mbps. Adaptive modulated OFDM system is promising technique for increasing the throughput. In the pilot symbol assisted high-speed packet transmission system, the data symbol duration is generally considered to be small compared to the coherence time. However, OFDM symbol duration is longer than the symbol duration of a single carrier system, so that the packet duration of the pilot symbol assisted high speed packet transmission system is long. In this case, the change of channel conditions is too fast to be accurately estimated by channel estimator at the receiver in high Doppler frequency, so that many errors occur during demodulation, especially with the data symbols at the end of each packet. In this paper, we consider the BER at various instantaneous E b /N 0 that includes the demodulation errors in high Doppler frequency. When the coherence time is ten times longer than the duration of a single packet, the channel can be closely approximated as an AWGN channel. Otherwise, the approximation breaks down and the above-mentioned errors that occur during demodulation must be taken into consideration. In this paper, we propose the pilot symbol assisted high speed packet transmission system based on adaptive OFDM using a novel lookup table to consider the demodulated errors and evaluate the throughput performance.

BER performance of OFDM system over frequency nonselective fast Ricean fading channels

The fast changing frequency nonselective Ricean fading channel introduces a complicated multiple distortion and an extra additive noise component for an OFDM system. The multiple distortion is the average of the sum of N(N/spl ges/3) correlated Ricean random variables. We propose an approximate technique for calculating the probability density function (PDF) of the multiple distortion under the assumption that the channel response changes in a linear fashion during one OFDM symbol. As a result, the bit error rate (BER) formula of a BPSK modulated OFDM system is derived. The results obtained using the derived formula describe well the OFDM performance under the time variant channel and match very well with the simulation results.