Existing speech semantic communication systems mainly based on Joint Source-Channel Coding (JSCC) architectures have demonstrated impressive performance, but their effectiveness remains limited by model structures specifically designed for particular tasks and datasets. Recent advances indicate that generative large models pre-trained on massive datasets, can achieve outstanding performance and exhibit exceptional effectiveness across diverse downstream tasks with minimal fine-tuning. To exploit the rich semantic knowledge embedded in large models and enable adaptive transmission over lossy channels, we propose a Large Speech Model enabled Semantic Communication (LargeSC) system. Simultaneously achieving adaptive compression and robust transmission over lossy channels remains challenging, requiring trade-offs among compression efficiency, speech quality, and latency. In this work, we employ the Mimi as a speech codec, converting speech into discrete tokens compatible with existing network architectures. We propose an adaptive controller module that enables adaptive transmission and in-band Unequal Error Protection (UEP), dynamically adjusting to both speech content and packet loss probability under bandwidth constraints. Additionally, we employ Low-Rank Adaptation (LoRA) to fine-tune the Moshi foundation model for generative recovery of lost speech tokens. Simulation results show that the proposed system supports bandwidths ranging from 550 bps to 2.06 kbps, outperforms conventional baselines in speech quality under high packet loss rates and achieves an end-to-end latency of approximately 460 ms, thereby demonstrating its potential for real-time deployment.

Motivated by the application of point-to-point communication networks and biological storage, we investigate new achievability bounds for noisy permutation channels with strictly positive and full-rank square matrices. Our new bounds use$\epsilon$-packing with Kullback-Leibler divergence as distance and are tighter than existing bounds. The key element is our analysis of the union set of error events. Additionally, Gaussian approximations of achievability bounds are derived, and the numerical evaluation shows the precision of the approximation.

Satellite communication systems play a crucial role in global communication networks due to their extensive coverage and efficient data transmission, but their physical layer security issues, especially in downlink transmission, are becoming increasingly prominent, making them vulnerable to illegal interception by malicious eavesdroppers. In this paper, we investigate the physical layer security enhancement of a multi-user satellite downlink transmission system assisted by hybrid reconfigurable intelligent surfaces (RIS) in the presence of multiple eavesdroppers. We aim to maximize the weighted sum secrecy rate (WSSR) of the satellite downlink transmission link subject to power constraints at both the satellite and the hybrid RIS. To resolve this non-convex optimization challenge, we propose an effective alternating optimization (AO) scheme by using the successive convex approximation (SCA) and particle swarm optimization (PSO) algorithm to jointly optimize the transmit beamforming matrix of the satellite and the reflection coefficient matrix of the hybrid RIS. Simulation results demonstrate the superior advantage of hybrid RIS in enhancing the secrecy performance of the satellite communication system when compared with the baseline schemes.

Thenoisy permutation channelis a useful abstraction introduced by Makur for point-to-point communication networks and biological storage. While the asymptotic capacity results exist for this model, the characterization of the second-order asymptotics is not available. Therefore, we analyze the converse bounds for the noisy permutation channel in thefinite blocklengthregime. To do this, we present a modified minimax meta-converse for noisy permutation channels by symbol relaxation and construct an auxiliary distribution for this bound usingdivergence covering. We then show the strong converse and refined asymptotic expansions. These two conclusions hold for noisy permutation channels with strictly positive matrices (entry-wise). In addition, we obtain computable bounds for the noisy permutation channel with the binary symmetric channel (BSC), including the original computable converse bound based on the modified minimax meta-converse, the asymptotic expansion, and the$\epsilon $-capacityresult. Finally, numerical results show that the normal approximation shows remarkable precision, and our new converse bound is stronger than existing bounds.

Abstract In this paper, a cooperative orthogonal frequency division multiplexing system with multiple untrusted amplify‐and‐forward relays is considered. Since there exists no direct link between source and user because of the shadowing effect, a positive system secrecy rate cannot be obtained. Addressing this issue, a cooperative user‐aided jamming technique to improve the secrecy performance is employed. With the aim of maximising the system secrecy rate, a joint resource allocation problem of power allocation, relay assignment and subcarrier pairing is formulated. By using the signal‐to‐noise ratio based approach and the Lagrange dual method, this nonconvex problem is solved efficiently. To reduce the calculation complexity, a suboptimal algorithm, which decouples the power allocation with the relay assignment and subcarrier pairing is further proposed. Numerical results are presented to demonstrate the advantage of the two proposed algorithms and the impact of relays' location and number of subcarriers on the secrecy performance. Moreover, it is shown that the secrecy performance of the proposed scheme is decreased with respect to the number of untrusted relays.

Abstract In this study, a non‐orthogonal multiple access based cooperative relay system is investigated, where the source serves multiple destinations via an amplify‐and‐forward relay. Direct links between the source and destinations are considered to form a general framework while the maximum ratio combination (MRC) is applied to obtain the largest decoding signal‐to‐interference‐plus‐noise ratio (SINR). Firstly, the outage performance is analysed with given successive interference cancellation (SIC) order and power allocation. An excellent approximated expression for the exact outage probabilities is derived in closed form. In addition, the asymptotic expression at high signal‐to‐noise ratio is provided to gain further insights. Then, in order to fully exploit the potential of the system, a joint optimisation of SIC order design and power allocation is formulated, with the objective of minimising the maximum outage probability of all destinations. By exploring the inherent property of the system, an optimal solution of SIC order and power allocation is developed. Finally, simulation results are presented to verify the correctness of the analytical results as well as indicate the efficiency of authors' SIC order design and power allocation algorithm.

This study investigates a problem of resource allocation for an uplink multi‐carrier non‐orthogonal multiple access (NOMA) system. To provide a general resource allocation problem, the order of successive interference cancellation (SIC), subcarrier assignment and power allocation are all considered as the optimisation variables of interest, with the objective of maximising the weighted sum rate under the transmit power constraint of each user equipment (UE). Firstly, a novel optimal SIC order is proposed based on the inherent structure of the uplink NOMA system. Then, with the optimal SIC order, the Lagrange dual method is employed to solve the joint subcarrier assignment and power allocation problem in an asymptotically optimal manner. In addition, an optimal solution of power allocation with a fixed subcarrier assignment is presented. In light of the optimal power allocation, a tight upper bound of the uplink NOMA system is developed by relaxing the number of multiplexed UEs on each subcarrier. Simulation results show that the proposed algorithm outperforms conventional orthogonal multiple access schemes and other static NOMA schemes, and as a benchmark, the upper bound reveals that multiplexing at most two UEs on each subcarrier is sufficient for the performance improvement.

The authors investigate the beamforming (BF) problem to minimise the power consumption for the downlink 2‐user multiple input single output‐based non‐orthogonal multiple access system. Inspired from the conventional zero‐forcing (ZF) scheme, they propose the Half‐ZF scheme which only mitigates the interference introduced by the signal of the cell‐interior user through the ZF method. Meanwhile, the interference introduced by the signal of the cell‐edge user is removed through the SIC technology. We derive the closed‐form expression for the BF vectors of the two users under the Half‐ZF scheme. The optimal power consumption for the Half‐ZF scheme is analysed and the corresponding solution of the BF factors are also obtained. Compared with the conventional ZF scheme, both the Half‐ZF scheme and the existing quasi‐degradation (QD) scheme can achieve lower power consumption than the ZF scheme. However, the Half‐ZF scheme can achieve this advantage under more relaxed conditions. Consequently, the Half‐ZF scheme consumes lower power than the QD scheme when combined with the ZF scheme in practical systems.

This article is focused on secure relay beamformer design with a correlated channel model in the relay-eavesdropper network. In this network, a single-antenna source-destination pair transmits secure information with the help of an amplify-and-forward (AF) relay equipped with multiple antennas, and the legitimate and eavesdropping channels are correlated. The relay cannot obtain the instantaneous channel state information (CSI) of the eavesdropper, and has only the knowledge of correlation information between the legitimate and eavesdropping channels. Depending on this information, we derive the conditional distribution of the eavesdropping channel. Two beamformers at the relay are studied for the approximate ergodic secrecy rate: (1) the generalized match-and-forward (GMF) beamformer to maximize the legitimate channel rate, and (2) the general-rank beamformer (GRBF). In addition, one lower-bound-maximizing (LBM) beamformer at the relay is discussed for maximizing the lower bound of the ergodic secrecy rate. We find that the GMF beamformer is the optimal rank-one beamformer, that the GRBF is the iteratively optimal beamformer, and that the performance of the LBM beamformer for the ergodic secrecy rate gets close to that of the GRBF for the approximate secrecy rate. It can also be observed that when the relay has lower power or the channel gain of the second hop is low, the performance of the GMF beamformer surpasses that of the GRBF. Numerical results are presented to illustrate the beamformers’ performance.