Daryus Chandra

Quantum-Aided Multi-User Transmission in Non-Orthogonal Multiple Access Systems

With the research on implementing a universal quantum computer being under the technological spotlight, new possibilities appear for their employment in wireless communications systems for reducing their complexity and improving their performance. In this treatise, we consider the downlink of a rank-deficient, multi-user system and we propose the discrete-valued and continuous-valued quantum-assisted particle swarm optimization (PSO) algorithms for performing vector perturbation precoding, as well as for lowering the required transmission power at the base station (BS), while minimizing the expected average bit error ratio (BER) at the mobile terminals. We use the minimum BER criterion. We show that the novel quantum-assisted precoding methodology results in an enhanced BER performance, when compared with that of a classical methodology employing the PSO algorithm, while requiring the same computational complexity in the challenging rank-deficient scenarios, where the number of transmit antenna elements at the BS is lower than the number of users. Moreover, when there is limited channel state information feedback from the users to the BS, due to the necessary quantization of the channel states, the proposed quantum-assisted precoder outperforms the classical precoder.

Unity-rate codes maximize the normalized throughput of on–off keying visible light communication

In this letter, we aim for maximizing the throughput of a visible light communication (VLC) system. Explicitly, we conceive a soft-in soft-out decoder providing soft feedback for the classic run length limited (RLL) codes, hence facilitating iterative decoding for exchanging valuable extrinsic information between the RLL and the error correction modules of a VLC system. Furthermore, we propose a unity rate code for our VLC system, which, hence, becomes capable of matching the ON–OFF keying capacity, while maintaining a flicker-free dimming value of 50%.

Quantum Error Correction Protects Quantum Search Algorithms Against Decoherence

When quantum computing becomes a wide-spread commercial reality, Quantum Search Algorithms (QSA) and especially Grover’s QSA will inevitably be one of their main applications, constituting their cornerstone. Most of the literature assumes that the quantum circuits are free from decoherence. Practically, decoherence will remain unavoidable as is the Gaussian noise of classic circuits imposed by the Brownian motion of electrons, hence it may have to be mitigated. In this contribution, we investigate the effect of quantum noise on the performance of QSAs, in terms of their success probability as a function of the database size to be searched, when decoherence is modelled by depolarizing channels’ deleterious effects imposed on the quantum gates. Moreover, we employ quantum error correction codes for limiting the effects of quantum noise and for correcting quantum flips. More specifically, we demonstrate that, when we search for a single solution in a database having 4096 entries using Grover’s QSA at an aggressive depolarizing probability of 10−3, the success probability of the search is 0.22 when no quantum coding is used, which is improved to 0.96 when Steane’s quantum error correction code is employed. Finally, apart from Steane’s code, the employment of Quantum Bose-Chaudhuri-Hocquenghem (QBCH) codes is also considered.

Network Coding Aided Cooperative Quantum Key Distribution Over Free-Space Optical Channels

Realistic public wireless channels and quantum key distribution (QKD) systems are amalgamated. Explicitly, we conceive network coding aided cooperative QKD over free space optical systems for improving the bit error ratio and either the key rate or the reliable operational distance. Our system has provided a 55% key rate improvement against the state-of-the-art benchmarker.

EXIT-chart Aided Quantum Code Design Improves the Normalised Throughput of Realistic Quantum Devices

In this contribution, the Hashing bound of entanglement-assisted quantum channels is investigated in the context of quantum devices built from a range of popular materials, such as trapped ion and relying on solid state nuclear magnetic resonance, which can be modeled as a so-called asymmetric channel. Then, quantum error correction codes (QECC) are designed based on extrinsic information transfer charts for improving performance when employing these quantum devices. The results are also verified by simulations. Our QECC schemes are capable of operating close to the corresponding Hashing bound.

Fully-Parallel Quantum Turbo Decoder

Quantum turbo codes (QTCs) are known to operate close to the achievable Hashing bound. However, the sequential nature of the conventional quantum turbo decoding algorithm imposes a high decoding latency, which increases linearly with the frame length. This posses a potential threat to quantum systems having short coherence times. In this context, we conceive a fully-parallel quantum turbo decoder (FPQTD), which eliminates the inherent time dependences of the conventional decoder by executing all the associated processes concurrently. Due to its parallel nature, the proposed FPQTD reduces the decoding times by several orders of magnitude, while maintaining the same performance. We have also demonstrated the significance of employing an odd-even interleaver design in conjunction with the proposed FPQTD. More specifically, it is shown that an odd-even interleaver reduces the computational complexity by 50%, without compromising the achievable performance.

Research Data: Air-to-ground NOMA Systems for the “Internet-Above-the-Clouds”

The dataset for the paper published in IEEE Access by Panagiotis Botsinis et al: Air-to-ground NOMA Systems for the “Internet-Above-the-Clouds”

Duality of Quantum and Classical Error Correction Codes: Design Principles and Examples

Quantum error correction codes (QECCs) can be constructed from the known classical coding paradigm by exploiting the inherent isomorphism between the classical and quantum regimes, while also addressing the challenges imposed by the strange laws of quantum physics. In this spirit, this paper provides deep insights into the duality of quantum and classical coding theory, hence aiming for bridging the gap between them. Explicitly, we survey the rich history of both classical as well as quantum codes. We then provide a comprehensive slow-paced tutorial for constructing stabilizer-based QECCs from arbitrary binary as well as quaternary codes, as exemplified by the dual-containing and non-dual-containing Calderbank–Shor–Steane (CSS) codes, non-CSS codes and entanglement-assisted codes. Finally, we apply our discussions to two popular code families, namely to the family of Bose–Chaudhuri–Hocquenghem as well as of convolutional codes and provide detailed design examples for both their classical as well as their quantum versions.

Unary-Coded Dimming Control Improves ON-OFF Keying Visible Light Communication

An ideal visible light communication (VLC) system should facilitate reliable data transmission at high throughputs, while also providing flicker-free illumination at the user-defined dimming level. In this spirit, we conceive a unary code aided dimming scheme for ON-OFF keying (OOK) modulated VLC systems. The proposed unary-coded scheme facilitates joint dimming and throughput control, while relying on iterative decoding. It is demonstrated that the proposed unary-coded dimming scheme provides attractive throughput gains over its contemporaries and it is also capable of approaching the theoretical throughput limit. Furthermore, we design novel joint dimming-forward error correction coding schemes, which significantly outperform their compensation time dimming-based counterparts in terms of the attainable bit error rate performance as well as the throughput. Finally, in the quest for approaching the capacity, we also optimize our system using EXTRINSIC information transfer charts and demonstrate an SNR-gain of upto 6 dB over the compensation time dimming-based classic benchmarker.

Joint-Alphabet Space Time Shift Keying in mm-Wave Non-Orthogonal Multiple Access

Flexible modulation schemes and smart multiple-input multiple-output techniques, as well as low-complexity detectors and preprocessors may become essential for efficiently balancing the bit error ratio performance, throughput, and complexity tradeoff for various application scenarios. Millimeter-Wave systems have a high available bandwidth and the potential to accommodate numerous antennas in a small area, which makes them an attractive candidate for future networks employing spatial modulation and space-time shift keying (STSK). Non-Orthogonal Multiple Access (NOMA) systems are capable of achieving an increased throughput, by allowing multiple users to share the same resources at the cost of a higher transmission power, or an increased detection (preprocessing) complexity at the receiver (transmitter) of an uplink (downlink) scenario. In this paper, we propose the new concept of joint-alphabet space time shift keying. As an application scenario, we employ it in the context of the uplink of NOMA mm-Wave systems. We demonstrate with the aid of extrinsic information transfer charts that a higher capacity is achievable when compared with STSK, while retaining the attractive flexibility of STSK in terms of its diversity gain and coding rate. Finally, we conceive quantum-assisted detectors for reducing the detection complexity, while attaining a near-optimal performance, when compared with the optimal iterative maximum A posteriori probability detector.