Secure Throughput Optimization of Selective Decode-and-Forward with Finite Blocklength

This paper proposes a scalable and energy-efficient scheduling framework tailored for massive machine-type communications (mMTC) in future 6G networks. Motivated by the dual challenges of massive connectivity and strict energy constraints, we introduce a new cooperative multi-cell uplink scheme that jointly optimizes user scheduling, power allocation, and interference management under finite block length (FBL) constraints. While prior studies have explored energy efficiency (EE) or connectivity separately, they often neglect FBL effects and lack scalable, interference-aware coordination across multi-cell NOMA deployments. Leveraging non-orthogonal multiple access (NOMA), our framework addresses both intra- and intercell interference through a multi-objective optimization problem that simultaneously maximizes EE and connectivity. To solve the problem, we develop the Sustainable and Reliable Scheduling for Massive Machine Type Communication using NOMA (SRS-MTCN) algorithm, integrating channel-aware user clustering, interference-aware resource allocation, and iterative power optimization. Simulation results demonstrate that the proposed approach performs significantly better than state-of-the-art baselines in dense deployments, achieving up to 35 – 58% EE improvement in medium-density regimes (16 – 32 devices/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>), while ensuring robust scalability and reliability in ultra-dense scenarios exceeding 40 devices/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. These results illustrate its suitability for sustainable 6G mMTC networks operating under FBL and energy constraints.

Data center networks (DCNs) require a low-cost, low-power optical transceiver to handle increased traffic from generative artificial intelligence, video streaming services, and more. Improving the required signal-to-noise ratio (RSNR) by digital signal processing such as forward error correction (FEC) mitigates the requirements for electrical and optical components. The optical transceivers in DCNs exploit a low-complexity soft-decision (SD) FEC, consisting of short block-length linear error-correcting codes and a low-complexity SD decoder (SDD), such as Chase decoding and ordered statistics decoding. The low-complexity SDD efficiently approaches a maximum likelihood decoding (MLD). However, the decoding performance of MLD is limited by its finite block length. In this paper, we describe the details of our proposed channel-polarized multilevel coding with iterative decoding (CP-MLC-ID). The proposed CP-MLC-ID improves the decoding performance by extending the codeword length to weakly and indirectly connect codewords via bypassed bits. The 19.5% –OH CP-MLC-ID using 128-bit extended Bose–Chaudhuri–Hocquenghem (eBCH) and KP4 codes outperforms the concatenated eBCH and KP4 codes with a net coding gain of 0.25 and 0.40dB for the same and double the number of SDDs, respectively. We also investigate the dependency of the decoding performance on the size of a bit interleaver. The performance degradation of CP-MLC-ID using an 8-bit interleaver is about 0.1dB compared to using the large-bit interleaver. Our results indicate that even a weak connection by exclusive-OR between codewords improves the decoding performance, compared to simple concatenated codes in the DCNs.

We propose a robust resource allocation framework to provide physical layer security for a multiple input single output (MISO) communication system. In the considered system, we assume that the both legitimate receiver and eavesdropper are in full-duplex (FD) mode and compare the corresponding performance to conventional cooperative jamming frameworks where a half-duplex (HD) receiver is at hand. In the present paper, the adversary intends to optimize its transmit and jamming signal parameters so as to minimize the MISO secrecy rate between the legitimate transmitter and receivers. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. Moreover, we investigate robustness against channel state information uncertainty. Optimal power allocation is obtained based on worst-case secrecy rate maximization, under legitimate transmitter power constraint in the presence of an active eavesdropper. Numerical results are then provided to confirm the advantages of using FD receivers.

In this work, we obtain lower and upper bounds on the maximal {transmission} rate at a given codeword length $n$, average probability of error $\epsilon$ and power constraint $\bar{P}$, over a finite valued, block fading additive white Gaussian noise (AWGN) channel with channel state information (CSI) at the transmitter {and the receiver}. {These bounds characterize} deviation of the finite blocklength coding rates from the channel capacity which is in turn achieved by the \textit{water filling} power allocation across time. {The bounds obtained also} characterize the rate enhancement possible due to the {CSI} at the transmitter in the finite blocklength regime. The results are further elucidated via numerical examples.

This paper investigates a cross-layer design to secure a set of buffered legitimate source nodes wishing to communicate with a common destination node. We assume a slotted-system and time-division multiple-access spectrum sharing where only one legitimate source node is allowed to transmit in a given time slot. The users' assignment probabilities to the time slots are optimized to satisfy a certain quality-of-service (QoS) requirement for all the legitimate source nodes. These probabilities are shown to be functions of the system parameters, secrecy rate outage probabilities, and arrival rates to the users' queues. To further improve the system's security and maximize the network performance measured by QoS metrics, i.e., secure stable-throughput region, we propose and compare beamforming-based cooperative jamming schemes that depend on the availability of the eavesdropper's instantaneous channel state information at the legitimate nodes. Each of the jamming schemes results in a different set of secrecy outage probabilities for the legitimate users which vary the time-assignment probabilities. We derive the secrecy stable- throughput region of the investigated wireless network. Our proposed jamming schemes achieve significant increase in the secure throughput over the fixed-jamming and no-jamming schemes.

This paper considers the downlink of an ultra-reliable low-latency communication (URLLC) system in which a base station (BS) serves multiple single-antenna users in the short (finite) blocklength (FBL) regime with the assistance of a reconfigurable intelligent surface (RIS). In the FBL regime, the users' achievable rates are complex functions of the beamforming vectors and of the RIS's programmable reflecting elements (PREs). We propose the joint design of the transmit beamformers and PREs to maximize the geometric mean (GM) of these rates (GM-rate) and show that this approach provides fair rate distribution and thus reliable links to all users. A novel computational algorithm is developed, which is based on closed forms to generate improved feasible points. Simulations show the merit of our solution.

In this paper, we investigate the ergodic performance of rate-splitting multiple access (RSMA) with finite blocklength (FBL) in high mobility communication systems to meet the ultra-reliable and low-latency (URLLC) requirements. Considering the imperfect channel state information at the transmitter (CSIT) originating from the high mobility of vehicles and the time delay of channel feedback, we analyze the statistical properties of signal-to-interference-plus-noise ratios (SINRs) for common and private streams at the desired vehicle. Next, we derive the closed-form expression for the ergodic sum-rate in FBL RSMA systems considering an arbitrary number of transmit antennas, number of vehicles, vehicle speeds, blocklengths, and block error rates (BLERs). Compared to other benchmarks, such as FBL non-orthogonal multiple access (NOMA) and space division multiple access (SDMA), the proposed scheme holds its optimum performance to meet the stringent BLER requirement while maintaining a prominent reduction in blocklength.

Information theoretic security has recently emerged as an effective physical layer approach to provide secure communications. The outage performance of such a secrecy communication system is considered in this paper, since it is an important criterion to measure whether users' predefined quality of service can be met. Provided that the legitimate receiver and eavesdropper have the same noise power, many existing secure schemes cannot achieve outage probability approaching zero, regardless of how large the transmission power is. By introducing cooperative transmission into secrecy communication systems, it will be shown here that outage probability approaching zero can be achieved. In particular, scenarios with single-antenna nodes and multiple-antenna nodes will both be addressed, and the optimal design of beamforming/precoding will be investigated. Explicit expressions of the achievable outage probability and diversity-multiplexing tradeoff will be developed to demonstrate the performance of the proposed cooperative secure transmission schemes, and numerical results are presented.

Cooperative transmission is an emerging communication technique that takes advantages of spatial diversity and broadcast natures of wireless channels to improve wireless channel capacity. However, cooperative transmission can be vulnerable to malicious attacks, especially in its current design. In this paper, we examine whether the cooperative transmission still have performance advantages when we consider the security issues. In particular, we identify various attacks against cooperative transmission, analyze the vulnerabilities of current schemes, design a trust-assisted cooperative transmission scheme, and evaluate the proposed scheme through analysis and simulations. The proposed scheme can fix the security problems and maintain the performance advantage. It performs much better than the traditional scheme when there are malicious/greedy relays or severe channel estimation errors. In addition, we investigate the advantage of cooperative transmission in terms of defending bad mouth attacks. A recovery of link bit error rate is observed.

The impact of unavailable relays is a serious issue in cooperative communication schemes, where the operation state of relays affects optimal relay selection. In addition, secure signal transmission is an interesting approach to prevent the wiretapping actions of eavesdropper nodes in a wireless environment. In this paper, we propose two cooperative secrecy transmission schemes: a secrecy decode-and-forward protocol and a hybrid of direct secrecy and cooperative secrecy transmission schemes to enhance the spectrum utilization efficiency. In the proposed schemes, a source transmits data signals to a destination with the assistance of relays. At the same time, these data signals are eavesdropped by another node. The best relays are successfully selected in a safe manner based on both decoding from a source to a destination and the available state of cooperative relays. The secrecy performance of each scheme is analyzed and evaluated by the exact outage probability over Rayleigh fading channels. Monte Carlo simulations were performed to verify the theoretical analysis. Finally, a discussion and comparison of the cooperative secrecy transmission schemes and the direct secrecy transmission approach are presented.

Underwater acoustic channels normally have low data rate, long propagation delay, severe multipath effect, and time varying fading. Cooperative transmission is a new wireless communication technique in which diversity gain is achieved by utilizing relay nodes as virtual antennae. In this paper, we investigate cooperative transmission techniques for underwater acoustic communications. First, we study the performance of several cooperative transmission schemes, originally designed for radio communications, in an underwater scenario. Second, by taking advantage of the low propagation speed of sound, we design a new wave cooperative transmission scheme. In this scheme, the relay nodes amplify the signal received from the source node, and then forward the signal immediately to the destination. The goal is to alter the multipath effect at the receiver. Third, we derive the performance upper bound for the proposed wave cooperative transmission scheme. The simulation results show that the proposed wave cooperative transmission has significant advantages over the traditional direct transmission and the existing cooperative transmission schemes originally designed for radio wireless networks.

Consumer electronics can support sixth-generation (6G) systems and their services, including ultra-reliable and low-latency communications (URLLC). In this context, unmanned aerial vehicles (UAVs) have become increasingly popular because they can: be dynamically positioned, take advantage of channel gains, and communicate directly via line-of-sight. UAVs, on the other hand, are unable to maintain a stable flight for prolonged periods of time and suffer from jittering impairments caused by strong winds. As a result of atmospheric conditions and environmental interference, the perfect channel state information (CSI) becomes obsolete. The aim of this study is to propose a power-efficient resource allocation scheme for URLLC-enabled UAV communication systems under finite block lengths, imperfect CSIs, and adverse jittering effects caused by wind. This involves optimizing UAV positioning and blocklength distribution together. Additionally, we propose a perturbation-based semidefinite programming (SDP) approach to reduce the sum power and demonstrate that it outperforms fixed benchmark algorithms. As such, it can reach power savings up to 77.18% compared to fixed benchmark algorithms. Our extensive simulation results demonstrate that our approach performs similarly to the exhaustive search and has low complexity. Thus, the proposed method thus provides a practical power-efficient URLLC implementation for memory-constrained UAV networks.

Physical layer security is a crucial issue in wireless networks to prevent legitimate communication from eavesdropping. This paper investigates the physical layer security of a wireless multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system in the presence of a multiple-antenna eavesdropper. We first propose a minimum mean square error (MMSE)-based-filter secure MIMO–OFDM system which can destroy the orthogonality of eavesdropper’s signals. The MMSE-based-filter is used at the receiver to suppress the inter-subcarrier interference and disturb the reception of eavesdropper while maintaining the quality of legitimate transmission. Next, we propose another artificial noise (AN)-assisted secure MIMO–OFDM system to further improve the security of the legitimate transmission. The time-domain AN signal is designed to be canceled out at the legitimate receiver. Therefore, AN will disturb the reception of eavesdropper while the legitimate transmission will not be affected. Finally, power allocation for AN signals and subcarriers will be discussed since AN is generated utilizing the residual power of the MIMO–OFDM system. Simulation results are presented to demonstrate the security performance of the proposed transmit filter design and AN-assisted scheme in the MIMO–OFDM system.

In this paper, we discuss non-binary polar codes using a 2×2 matrix over a Galois field GF(2q) as the kernel. Conventional construction of non-binary polar codes divides the synthesized channels into frozen channels and information channels. Each information channel carries one symbol, i.e., q bits. However, there are many middle channels with insufficient polarization, which cannot carry one symbol of q bits but only i bits, 1≤i<q,i∈Z, at finite block length. In this paper, we consider bit-level construction for multiplicative repetition (MR)-based non-binary polar codes and propose a bit-level construction based on the two following methods. We first calculate the error probability and channel capacity lower bound of each synthesized channel based on the channel degradation method, and then determine both the number and index of the carried bits for each synthesized channel according to the symbol error probability and capacity. To reduce complexity, we also introduce a Monte-Carlo method. We compute the error probability of each synthesized channel carrying i information bits and select the optimal construction that can minimize the union bound of the error probability. Finally, an improved construction-based probabilistic shaping method for MR-based non-binary polar codes is considered. Simulation results show that the proposed construction significantly improved the decoding performance compared with the conventional construction scheme.

Pilot-assisted channel training for acquiring the channel state information (CSI) is a very critical functionality in URLLC to ensure reliable data transmission. In this paper, we consider the joint uplink and downlink URLLC transmission in which the source uploads a packet to the BS, and then BS forwards this packet to the destination. CSI in the uplink can be estimated at BS by sending a training pilot from source while for the downlink, an extra codebook-based channel quantization is required at destination to measure the estimated channel and feedback the limited-precision results to BS for beamforming before data transmission. This could bring about channel estimation errors, quantization errors and decoding errors, respectively caused by limited training symbols, limited feedback overheads and finite blocklength. In view of this, we for the first time investigate the transmission performance of URLLC under this circumstance and design a performance optimization framework to maximize the transmission reliability. Particularly, the impact of channel estimation accuracy on the transmission reliability of URLLC is studied based on the finite blocklength information theory. An analytical closed-form expression of transmission error probability under imperfect CSI is also derived with respect to key parameters, like the training pilot length, feedback bits and data transmission durations. By jointly optimizing those parameters, we could derive the maximum transmission reliability. Simulation results are provided to validate the effectiveness of our proposed performance optimization framework.