Soft-Output Detector Using Multi-Layer Perceptron for Bit-Patterned Media Recording

As conventional data storage systems are faced with critical problems such as the superparamagnetic limit, bit-patterned media recording (BPMR) has received significant attention as a promising next-generation magnetic data storage system. However, the reduced spacing between islands at increased areal density causes severe intersymbol and intertrack interference, which degrade BPMR system performance. In this study, we introduce a soft-output detector using multi-layer perceptron to predict reliable information. A received signal is equalized and detected by the MLP detector. The MLP detector provides a well-estimated value by using the binary-cross entropy function as a loss function and the identity function as an activation function for the output layer of the MLP detector. This study investigates the received probability distributions out of the detectors and compares the performance of various versions against a conventional detector. Compared with the conventional detection, the proposed MLP detectors provide a small variance and better BER performance than the conventional detection. Simulations of MLP designs show an advantage over conventional detection. Moreover, the proposed MLP detectors with the demodulator exhibit better BER performance than the conventional detector with the demodulator.

BER-Aware Reflecting Elements Allocation for RIS-aided NOMA Networks over Ricean Fading

Reconfigurable intelligent surface (RIS) as a supportive technology for aiding downlink non-orthogonal multiple access (NOMA) can enhance the bit error rate (BER) performance. In this paper, a novel BER-aware reflecting elements allocation (REA) on an RIS is proposed to maintain the BER order among paired RIS-NOMA users. The RIS REA is useful for minimizing the average user BER, ompared with a system that allocates the same number of elements to all users. Additionally, the Ricean fading is considered instead of Rayleigh fading as it is more practical and general. Furthermore,an REA optimization objective function for equalizing the user BER is proposed. In order to solve the problem, a modified exhaustive search is proposed to reduce complexity. The distribution of the objective function is observed first; subsequently, the exhaustive search range is determined. Both the analytical and simulation results show that the proposed algorithm can minimize the average user BER.

BER-Aware Reflecting Elements Allocation for RIS-aided NOMA Networks over Ricean Fading

Reconfigurable intelligent surface (RIS) as a supportive technology for aiding downlink non-orthogonal multiple access (NOMA) can enhance the bit error rate (BER) performance. In this paper, a novel BER-aware reflecting elements allocation (REA) on an RIS is proposed to maintain the BER order among paired RIS-NOMA users. The RIS REA is useful for minimizing the average user BER, ompared with a system that allocates the same number of elements to all users. Additionally, the Ricean fading is considered instead of Rayleigh fading as it is more practical and general. Furthermore,an REA optimization objective function for equalizing the user BER is proposed. In order to solve the problem, a modified exhaustive search is proposed to reduce complexity. The distribution of the objective function is observed first; subsequently, the exhaustive search range is determined. Both the analytical and simulation results show that the proposed algorithm can minimize the average user BER.

Improving BER Performance of Massive MIMO Scheme over Rayleigh Fading Channel

In massive multiple input multiple output (mMIMO) scheme, the system capacity can be improved without additional bandwidth or transmit power by using a huge antenna array at base station with as much separation between antenna elements as possible. Unfortunately, its performance depends on having a perfect channel state estimate between the base state and the users. In this paper, the bit error rate (BER) performance of a mMIMO scheme is improved using genetic algorithm-based optimization with simulation performed in MATLAB software environment. The genetic algorithm used selects the best signal required for effective transmission. Four different antenna configurations in the order of 2x2, 4x4, 8x8 and 16x16 were considered for the simulation. The encoding and decoding were done using an STBC coded. Also, filter bank multicarrier-offset quadrature amplitude modulation (FBMC-OQAM) scheme was used and simulation was carried out for 4-FBMC-OQAM, 16 FBMC-OQAM, and 64 FBMC-OQAM order. The BER is computed for both the optimized and un-optimized mMIMO schemes, and the performance of both schemes is compared. Simulation results show a significant improvement in the BER of the optimized mMIMO compared to the normal (coded) MIMO scheme. The overall results show that the optimized mMIMO experience a reduced BER when compared to the normal mMIMO. In both cases, the BER reduces gradually as the number of antenna increases.

MIMO-Filtered OFDM System Improvement Using Modified Concatenated RS/LDPC Codes

In mobile communication systems, there are errors that will be generated in the digital signal due to fading and interference. Consequently, different techniques are used to improve the system's reliability and enhance the signal's robustness. Channel coding techniques are used to enhance the system reliability of 5G wireless communication systems . In the upcoming wireless technologies, LDPC codes are still introduced as an alternative to turbo codes. However, the error floor phenomenon is one of the biggest demerits of using LDPC code in the different communication systems that need low error rates. This paper uses RS codes with LDPC codes in a concatenated code to solve this demerit of LDPC codes. Meanwhile, a modified concatenated RS/LDPC codes are created using outer RS codes with inner LDPC codes then appended by interleaver, unlike the conventional concatenated codes that use the interleaver between both codes. Thereafter, the modified concatenated RS/LDPC codes were suggested to enhance BER performance for the f-OFDM system. The results showed that using the proposed concatenated code outperformed using single and familiar concatenated RS/LDPC code in terms of improving BER performance. Meanwhile, the proposed system achieved lower OOBE values than the conventional OFDM system. Therefore, the resulted system can be introduced as a competitor candidate for 5G wireless communication systems due to these features

Spectral Analysis of (Multi-) Pulse-Position Modulation

Nowadays, laser communication has received great achievements owing to its advantages, e.g., large channel capacity, easy miniaturization of communication system and strong anti-interference ability in different conditions. Pulse position modulation (PPM), as an important modulation technology in laser communication system that transmit signal with lower power, is attracting much attention. However, the performance of the modulation scheme highly depends on the bandwidth of transmission. To remedy this defect of PPM, the multipulse position modulation (MPPM) scheme is proposed to increase the accuracy and bandwidth limit. This modulation scheme has stronger anti-interference ability than PPM. Therefore, there has been rising interest in studying the characteristics of the multi-PPM. In this article, we developed an appropriate mathematical model to represent a PPM transmission, analyzed the spectrum of the transmission and characterized the bandwidth of this transmission. Compared with benchmarks of MPPM scheme, its performance has been discussed. According to the analysis, MPPM strongly increases band-utilization efficiency, however PPM has a better bit error rate (BER) performance than MPPM.

Null Subcarrier Index Modulation in OFDM Systems for 6G and Beyond

Computational complexity is one of the drawbacks of orthogonal frequency division multiplexing (OFDM)-index modulation (IM) systems. In this study, a novel IM technique is proposed for OFDM systems by considering the null subcarrier locations (NSC-OFDM-IM) within a predetermined group in the frequency domain. So far, a variety of index modulation techniques have been proposed for OFDM systems. However, they are almost always based on modulating the active subcarrier indices. We propose a novel index modulation technique by employing the part of the transmitted bit group into the null subcarrier location index within the predefined size of the subgroup. The novelty comes from modulating null subcarriers rather than actives and reducing the computational complexity of the index selection and index detection algorithms at the transmitter and receiver, respectively. The proposed method is physically straightforward and easy to implement owing to the size of the subgroups, which is defined as a power of two. Based on the results of our simulations, it appeared that the proposed NSC-OFDM-IM does not suffer from any performance degradation compared to the existing OFDM-IM, while achieving better bit error rate (BER) performance and improved spectral efficiency (SE) compared to conventional OFDM. Moreover, in terms of computational complexity, the proposed approach has a significantly reduced complexity over the traditional OFDM-IM scheme.