This paper investigates near-field channel effects in a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)–assisted uplink system with a multi-antenna base station. The considered system is based on generalized non-orthogonal multiple access (NOMA) with imperfect successive interference cancellation (SIC), encompassing space division multiple access (SDMA) and NOMA with perfect SIC as special cases. For this general setting, we develop sum-rate maximization algorithms with and without quality-of-service (QoS) constraints using an alternating optimization (AO) framework and a penalty-based nonlinear optimization (NLO) method, providing flexible performance–complexity trade-offs. We also derive an upper bound on the achievable sum rate to characterize multiplexing and beamforming gains under both near- and far-field channel conditions. The results show that AO initialized with the proposed NLO solution achieves the best performance with moderate computational complexity, aligning well with the upper-bound behavior. Furthermore, analysis and simulations demonstrate that near-field channels increase the available degrees of freedom and provide enhanced robustness to imperfect SIC and QoS constraints.

Integrated sensing and communication (ISAC) technology presents promising prospects for improving spectral efficiency, enabling hardware resource sharing, and facilitating novel application scenarios. Nevertheless, the mutual interference between communication and sensing remains a critical barrier to overcome. As an effective interference management solution, both non-orthogonal multiple access (NOMA) and rate splitting multiple access (RSMA) demonstrate unique advantages in interference suppression, which are expected to substantially enhance the overall performance of ISAC systems. To this end, the design options of NOMA versus RSMA for the ISAC systems are investigated in this paper. Furthermore, due to the inherent complexities in both signal propagation characteristics and receiver processing architectures, channel estimation errors (CEEs) and imperfect successive interference cancellation (ipSIC) are incorporated during system modeling. Against the above background, the communication and sensing performance of the NOMA and RSMA ISAC systems is analyzed by respectively deriving the exact and asymptotic outage probabilities (OPs) and ergodic rates (ERs) for the users, the probability of detection (PoD) for the base station and Cramér-Rao bound (CRB). The numerical results demonstrate that RSMA outperforms NOMA in terms of OPs, ERs, PoD, and CRB.

A novel mobile edge generation (MEG) framework is proposed to efficiently operate large models at edge networks for low-latency image generation. The generation of large-scale image content is split into two parts, namely primary and secondary regions, with an adjustable generation splitting ratio. The primary region is generated by a large generative model (LGM) at the edge cloud and then transmitted to the mobile device, whereas the remaining secondary regions is created by a tiny generative model (TinyGM) at the mobile device, thus reducing transmission and computation overheads. Both single-user and multi-user cases are considered to characterize the tradeoff between mobile energy consumption and generation delay. For the single-user case, a multi-objective programming (MOP) is formulated for the joint optimization of generation splitting and mobile power control, which simultaneously minimizes the generation delay and mobile energy consumption. This MOP is transferred into single-objective optimization using the ϵ-constraint method. The closed-form optimal solution is derived to obtain Pareto-optimal energy-delay (E-D) region. It is revealed that MEG achieves significant performance gains then conventional fully edge generation (FEG) when signal-to-noise ratio (SNR) or mobile generative cost is low. For the multi-user case, a joint generation splitting and resource allocation problem is formulated, which minimizes the maximum generation delay subject to ϵ-bounded mobile energy consumption and resource constraints. An McCormick-relaxation branch-and-bound (M-BnB) algorithm is proposed to obtain the globally optimal solution. Simulation results demonstrate the Pareto-optimal E-D region in single-user and multi-user cases. Furthermore, MEG flexibly reduces delay compared to conventional FEG and model split schemes while maintaining generative quality.

Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) have emerged as a promising technology for shaping wireless environments favorable to their supporting systems while providing full-space coverage. However, the path loss product of passive STAR-RISs necessitates the deployment of extremely large (XL)-STAR-RIS elements. We integrate an XL-STAR-RIS operating in energy-splitting mode into an uplink multiuser single-input multiple-output (SIMO) system to improve spectral efficiency. Our primary focus is to investigate the impact of the near-field channels between the XL-STAR-RIS and users on the sum rate. To this end, we propose a sum rate maximization algorithm that alternately optimizes XL-STAR-RIS beamforming and power allocation, leveraging closed-form power allocation through La-grangian dual and quadratic transforms using the optimal receive beamforming. Performance evaluation demonstrates the sum rate gains attributed to near-field effects by comparing the optimized sum rates in near-field and far-field channel models.

Wireless federated learning (FL) faces significant challenges due to limited wireless resources and unreliable channels. To cope with these challenges, this work proposes a gradient compensation-based FL approach (FL-GC), in which the edge server estimates the local gradients of transmission failure and unselected clients by first-order Taylor approximation based on previously received local gradients. We then theoretically analyze the convergence bound, which reveals that selecting clients with large local gradient staleness helps reduce the estimation error and improve learning performance. Based on this, we jointly optimize the client selection and resource allocation strategies to enhance the FL performance under resource-limited wireless networks. Simulation results under a typical data heterogeneity scenario demonstrate the efficacy of our proposed scheme in mitigating the adverse effects of unreliable transmission and limited resources. It improves 7.34% model accuracy compared to the considered benchmarks and is able to save 42.5% training time to achieve the target accuracy.

In this paper, we propose a wireless powered communication network (WPCN) employing active intelligent reflection surface (IRS) and nonorthogonal multiple access (NOMA) to support multiple battery-free devices. We aim to maximize the sum rate by incorporating practical issues such as amplifying power constraints of active IRS and a nonlinear energy harvesting (EH) model. Since jointly optimizing IRS beamforming in wireless power transfer (WPT), IRS beamforming in wireless information transfer (WIT), and time allocation (TA) is computationally challenging, we resort to an alternating optimization (AO) algorithm in a computationally efficient manner. Additionally, we propose a one-shot (OS) optimization approach for shared amplitude control that provides closed-form expressions for IRS beamforming in WPT and WIT to be computed at a low latency. This OS solution can also serve as the initial point of the proposed AO algorithm and is used for throughput analysis in line-of-sight channels. It is shown that the proposed AO algorithm reduces the complexity of the benchmark and our proposed OS approach, despite its low computational complexity, provides a performance comparable to that of the AO solution. It is also shown that the amplifying power limit of active IRS elements affects the performance severely while the effect of nonlinear EH is not so prominent. Furthermore, the results from analysis and simulation elucidate favorable system configurations for the active IRS-aided WPCN with NOMA when compared with its passive IRS counterpart.

To enhance the massive connectivity and spectral efficiency of Internet-of-Things applications supporting batteryless devices, we integrate active intelligent reflecting surface (IRS) into multiple input single output (MISO) wireless powered communication networks (WPCNs). The networks are designed with either nonorthogonal multiple access (NOMA) or time division multiple access (TDMA) towards the maximum throughput. For this purpose, we develop alternative optimization (AO) algorithms optimizing energy beamforming (BF) and active IRS BF in wireless power transfer, active IRS BF and receive BF in wireless information transfer, and time allocation iteratively, for both NOMA and TDMA networks. The proposed algorithm for the NOMA network solves each subproblem using either a convex optimization solver or a closed-form expression with the help of with the help of fractional programming. For TDMA networks, we develop a more computationally efficient algorithm than the conventional algorithm for the TDMA network. The results show that active IRS is more effective than passive IRS with a moderate number of IRS elements for MISO WPCNs. In addition, NOMA significantly outperforms TDMA for active IRS aided MISO WPCN although a slight gain of TDMA over NOMA is observed for the single-antenna counterpart.

We consider a simultaneous wireless transfer of information and power in a two-way relaying network, where a decode-and-forward protocol is employed for data exchange between two source devices at different rates. The data exchange is accomplished in two time phases (TPs) with possibly asymmetric TP ratios, where the relay is powered by the source devices in the first phase through simultaneous wireless information and power transfer (SWIPT) either by power splitting (PS) or by time switching (TS). For the network, resource allocation of the PS and TP ratios for the PS-based SWIPT and that of the TS and TP ratios for the TS-based SWIPT are studied to minimize the system outage probability. We first solve the joint optimization problem of each case with the instantaneous channel state information and then propose suboptimal schemes utilizing one or two values for the TP ratio to lower the implementation complexity. The results from analysis and simulation show that the proposed schemes outperform the benchmark scheme with equal resource allocation and that the gain gets more prominent as the rates of the data exchanged or the relay locations become more asymmetric.

This letter considers the downlink of a cellular network with an asymmetric antenna configuration, where virtual multiple-input multiple-output (MIMO) is formed with receive cooperation over out-of-band or in-band overlay device-to-device (D2D) links. The objective of this work is to determine the best pairing and resource sharing configuration of the cooperative devices such that the overall network utility is optimized and the devices achieve their best available rate larger than that without D2D cooperation. A distributed algorithm is developed via an algorithmic-game-theoretic message-passing framework to obtain a solution at a low computational cost and without reporting the D2D link qualities to the base station. We show that the algorithm converges to an optimal point through analysis and its performance is validated by simulation. In addition, the virtual MIMO network enabled by the D2D receive cooperation is shown to provide a significant gain over the network without the D2D receive cooperation.

A low-complexity design of multi-antenna relay processing is proposed for two-way relay networks with asymmetric data flows. The proposed scheme adopts three-phase (3P) analog network coding (ANC) which allows orthogonal transmission of two communicating nodes to overcome some disadvantages of two-phase (2P) ANC protocols. For the 3P ANC, we propose antenna selection at the relay to exploit the diversity without channel estimation and rate-aware relay power allocation (RPA) to improve the outage performance under the asymmetric rate requirements. The results show that the proposed scheme without or with RPA outperforms the conventional two-phase ANC significantly in various relay locations. It is also shown that the suboptimal RPA proposed for practical implementation provides a performance close to that of the optimal RPA.

A class of low-complexity multi-antenna relaying schemes is proposed for orthogonal frequency division multiplexing based one-way and two-way relay networks. In the proposed schemes, two single-antenna terminal nodes complete the data transfer in two time phases via a multi-antenna amplify-and-forward relay without channel state information, discrete Fourier transform (DFT), and inverse DFT. The relay signal processing consists of receive combining, power scaling, and transmit diversity, where instantaneous time domain power scaling is proposed for power scaling and power-based selection combining and cyclic delay combining are proposed for receive combining, to leverage the performance only with time domain operations. An approximation to the outage probability is also derived to predict the coded performance behavior under practical channel models. It is shown by evaluating the outage probability and coded bit error rate that the proposed schemes outperform the conventional schemes of comparable complexity.

We consider two-way relay (TWR) networks consisting of two communicating nodes and multiple relays built upon orthogonal frequency-division multiplexing signaling. For low-cost implementation of relays, two pragmatic TWR protocols are proposed based on analog network coding (ANC). The proposed two-phase (2P)- and three-phase (3P)-ANC schemes employ time-domain instantaneous power scaling and relay selection to improve the outage performance without equipping discrete Fourier transform (DFT) and inverse DFT functions at the relay. In particular, we devise a relay power allocation factor and a resultant relay selection metric for the proposed 3P-ANC scheme, which can be implemented at low complexity. For the proposed schemes, the outage probability and achievable diversity order are also analyzed, which reveals a larger diversity order of the 3P-ANC scheme than the 2P-ANC scheme. The results from analysis and simulation show that the proposed schemes outperform the conventional 2P-ANC schemes employing time-domain average power scaling and distributed space-time block coding or frequency-domain power scaling and relay selection.

This paper considers a relay system using two-layer superposition coding to minimize the expected distortion of a Gaussian source at the destination node. For the system, we propose two types of layer- selective relaying based on the local decoding result at the relay and the decoding result at the destination node fed back to the relay. One type of the proposed scheme uses decode-and-forward (DF) in the design of the relay signals, while the other type uses both DF and amplify-and-forward (AF). For the proposed scheme, we analyze the outage probabilities and evaluate the expected distortion according to the relay location. The results reveal that the proposed scheme improves the finite SNR performance, in particular when the relay node is closer to the source node than it is to the destination node.

We consider a relay network that delivers a Gaussian source by employing successive refinement source coding and superposition coding of layers at the source node and successive decoding at the relay and destination nodes. For the network, making use of the decoding results at the relay and destination nodes of the first transmission, an efficient relaying strategy of layers is proposed to minimize the expected distortion (ED) when only the average channel state information is available at the source node. Three types of the proposed scheme, defined as Prop-DF, using decode-and-forward signals, Prop-AF, using amplify-and-forward signals, and Prop-MF, using mixed-forward signals, are addressed and analyzed in terms of the outage probability and distortion exponent. Unlike other studies, we have also taken the relay location into account in deriving the distortion exponent showing the high SNR behavior of the ED. The results show that the proposed scheme increases the distortion exponent up to twice that of the conventional relaying schemes when the relay is close to the source node, and that Prop-MF provides the best performance for most relay locations.

The use of multiple-antenna arrays can leverage the physical-layer security of wireless systems. It is therefore important to characterize such systems in a realistic situation where we can apply the so-called artificial-noise solution in multiple-antenna systems to enhance the communication confidentiality by only exploiting a fading nature of wireless environments. In this paper, we consider secure communication over a multiple-input single-output Rayleigh-fading channel in the presence of a multiple-antenna eavesdropper-referred to as a multiple-input single-output multiple-eavesdropper (MISOME) wiretap channel. Specifically, secure beamforming with artificial noise is treated when the transmitter has access to full channel state information (CSI) of a legitimate channel but only channel distribution information of an eavesdropper channel. We first put forth a new notion of the symbol error probability (SEP) of confidential information-called the δ-secrecy SEP-to connect the reliability and confidentiality of the legitimate communication. We then quantify the diversity impact of secure beamforming with artificial noise on the δ-secrecy SEP in the MISOME wiretap channel and show that the artificial-noise strategy preserves the secrecy diversity of order nt- nefor nttransmit and neeavesdropper antennas.

This paper analyzes a two-way relaying (TWR) system where two sources with multiple antennas exchange data via an amplify-and-forward relay with a single antenna. In the system considered herein, the link quality between the sources and relay can generally be asymmetric due to the nonidentical antenna configuration and relay location. In such a general setup, an accurate upper-bound on the average sum rate (ASR) is derived when beamforming is employed at the sources. We show that the proposed bound is much closer to the exact ASR than the conventional bound under various system configurations. It is also observed that relay location is more important than relay power allocation when the numbers of source antennas are unequal.

This paper considers a two-way relaying (TWR) half-duplex network in which two users communicate each other with the help of a non-regenerative relay when the direct link between the two users is nonvanishing. For the network, we adopt three protocols each with two, three, or four phases either by using analog network coding (ANC) or amplify-and-forward. The performance of the protocols is analyzed by deriving tight bounds on the average sum rate (ASR) and the outage probability in a unified form. Both results from analysis and simulation show that the three-phase ANC for TWR is favored in the outage performance by trading the time resource with the diversity gain while the two-phase ANC is favored in the ASR performance.

This paper provides a low-complexity scheme for peak-to-average power ratio (PAPR) reduction without side information for frequency switched transmit diversity orthogonal frequency division multiplexing (FSTD-OFDM). The proposed scheme generates multiple signal candidates (SCs) by dividing parallel data symbols into subparts and mapping the subparts onto the antennas under a criterion reducing the correlation between the SCs to select one SC with minimum PAPR. The proposed scheme is shown to provide reasonably good PAPR performance at a lower complexity than the conventional schemes. In addition, the proposed scheme can detect the transmitted SC via energy detection without side information.

To reduce the influence of interference on the OFDM-based cognitive radio overlaid with narrowband primary users, we consider a scheme called the variable subband nulling (VSN), in which a VSN mode is selected adaptively according to the result of spectrum sensing for the frames following the sensing period. For reliable detection of the VSN mode embedded in the preamble, we consider two types of metrics. The performances of the metrics are analyzed in Gaussian channels with/without narrowband interference (NBI), and are confirmed by simulation results. In fading channels with/without NBI, the detection performance is examined via simulation results. The analysis and simulation results have confirmed that, if the VSN mode is selected appropriately at the transmitter, the proposed metrics provide us with a reliable detection performance even when the NBI is strong.

This paper presents an OFDM-based relay network with relay selection employing both decode-and-forward (DF) and amplify-and-forward (AF) approaches. For the network, we derive a lower-bound on the outage probability and the diversity order achievable in frequency selective fading channels. Simulation results show that both DF and AF relaying provides the diversity order same to that obtained from the lower-bound but DF relaying provides a SNR gain over AF relaying. It is also observed that the SNR gain of the DF gets larger as the channel diversity order increases, which makes DF relaying more favorable to the OFDM network with relay selection.

This paper presents a cross-layer design of adaptive modulation and coding (AMC) with truncated hybrid automatic repeat request (HARQ) for one-to-many multicast transmission, in order to increase the spectral efficiency under the quality-of-service (QoS) constraints. For adaptive transmission over the channel common to the multicast group users, the AMC mode is chosen with the minimum SNR among the users to guarantee the target performance of all users. In the meanwhile, the minimum SNR required to support an AMC mode is aggressively designed by allowing retransmission with HARQ schemes. For the proposed design, we derive the average packet error rate, average number of transmission, and spectral efficiency and provide the performance numerically obtained. Numerical results show that the cross-layer design for multicast provides a significant performance gain at a small number of retransmissions as in unicast. In particular, it is observed that AMC design with HARQ is more beneficial in the low SNR region where multicast performs worse than unicast.

This paper introduces a reconfigurable mixed frame structure and a resource allocation algorithm for OFDMA systems supporting both the band-AMC and diversity modes in the frame. To reduce the total feedback without significant performance loss, we assign a user to the diversity subchannel when the band-AMC mode has no gain over the diversity mode based on the frequency selectivity of the user. After user selection, we apply joint power and rate allocation to exploit the asymmetry in required transmit power of the band-AMC mode and the diversity mode. The results reveal that the mixed frame with simple user classification provides a performance comparable to the frame with band-AMC mode only at a much reduced feedback. In particular, it is observed that the mixed frame with frequency division is preferable to that with time division by increasing the throughput of the users at the cell boundary in a large cell.

This paper presents variable power and rate allocation (PRA) for a multiuser orthogonal frequency division multiple access code division multiplexing (OFDMA-CDM) system which exploits both orthogonality among users and symbol-level diversity. To predict the link performance, we analyze the postprocessing SNR as the transmit power (TP) varies when the minimum mean square error combiner (MMSEC) is employed. It is shown from analysis that the MMSEC SNR is nonlinear in TP, but is bounded by the harmonic and the arithmetic means of the subcarrier SNRs. From the observation, we propose two variable PRA methods using a simple channel quality indication and a required TP estimation method. Simulation results show that the proposed methods not only guarantee the target performance but also increase the throughput at the same or slightly increased feedback overhead compared with the fixed TP allocation case.

For the CR systems sharing the spectrum with narrowband primary devices, this paper presents an OFDM system supporting the fractional bandwidth (FBW) mode to avoid the interference to or from the primary devices. For the system, the preamble and FBW mode detection algorithm are provided to obtain the FBW mode information during the initial synchronization. The simulation results reveal that the FBW mode information can be obtained at the SNR region lower than Es/N0 = 0 dB. In addition, the FBW mode transmission and detection do not incur any deterioration of the synchronization performance.

Coded cooperation has been proposed to increase the diversity or cell coverage in the uplink of a cellular network. In the method, a relay transmits incremental redundancy (IR) of the source's codeword in cooperation stage. However, for a turbo coded system, IR is not always a best way especially when the first code segment is corrupted badly. Thus, we propose an adaptive cooperation method using different HARQ schemes by estimating the reliability of the first code segment. From simulation results, it is shown that the proposed method improves the performance irrespective of the SNR values of cooperating users.

Recently, broadcast and multicast services are introduced in cellular networks to deliver multimedia contents efficiently with limited wireless resources. To provide such services more reliably at the cell boundary, we propose a macro diversity coding method for an OFDM cellular system. In the method, cells are divided into multiple cell groups and a coded packet is partitioned into the subblocks for which different cell group combinations are assigned to transmit two diversity branches of a transmit diversity code. Thus, the service data rate is increased at the same transmit power due to the channel diversity of each transmit symbol and coding diversity obtained by different fading statistics over the subblocks

A search algorithm for stopping sets in a Tanner graph is proposed for designing good low-density parity-check (LDPC) codes. By applying the belief-propagation algorithm with messages containing the information of originated variable nodes and their connected edges, the stopping sets can be detected. Furthermore, a code design method using the algorithm is presented and the performances of the designed code over several channels are shown

In this paper, we propose an LDPC-coded OFDMA system with a resource allocation method suitable for the uplink of mobile cellular environments. At the receiver of the proposed system, an iterative channel estimation and decoding (IED) method with a Wiener filter adapting to the channel variation rate is employed to support high mobility without boosting the pilot power. For practical applications, the channel variation rate is also estimated with pilot symbols to select Wiener filter coefficients for every received packet dynamically allocated. It is shown that the proposed system supports the mobility up to 250 km/h and exhibits more than 1 dB performance gain over the system with conventional non-iterative receiver.

In this paper we propose low complexity turbo detection and decoding schemes for space-time block-coded block transmission (STBC-BT) systems. Because of the circulant property of the channel matrices, the detectors can be implemented in the frequency domain. Simulation results show that the performance of the proposed receivers is better than that of the traditional, noniterative receivers.

This paper presents a turbo coded multicarrier direct sequence code division multiple access (DS/CDMA) system, where the outputs of a turbo encoder are repetition coded at multiple rates and transmitted in parallel over a number of subchannels. A performance bound useful in the so-called error floor region is obtained for Rayleigh fading channels when different diversity orders are given to each turbo code symbol. Simulation results are also provided for the low signal-to-noise ratio (SNR) region where the bound is not applicable. It is observed that the error floor can be lowered, with some performance loss in the low SNR region, by applying nonuniform repetition coding to the turbo code symbols.

We consider the quasi-maximum-likelihood (quasi-ML) detectors of the reverse link system that uses antenna arrays in asynchronous channels when the channel vector is time-invariant and time-varying. A channel vector estimation method based on eigendecomposition for time-invariant channels and its adaptive version suitable for the time-varying channels are also proposed. It is shown that the proposed quasi-ML detector can be regarded as a beamformer followed by a decorrelating filter and that the proposed system performs better than the conventional decorrelator scheme. It is also observed that the performance gain of the proposed scheme over the conventional decorrelator system increases as the numbers of active users and antenna arrays increase.

An efficient implementation of the D-homomorphism for generating de Bruijn (1946) sequences is presented. The number of exclusive-or operations required to generate the next bit for de Bruijn sequences of order n from a de Bruijn function of order k is shown to be approximately k(2/sup W(n-k)/-1), where W(r) is the number of one's in the binary representation of r: therefore, the number of required operations can be reduced to k if the de Bruijn function is selected appropriately. As an application, the stream cipher is indicated.

A vector channel model is proposed and some statistical properties of the asymptotic efficiency of the decorrelating detector with base-station antenna arrays are investigated. It is shown that we can get gain over the conventional decorrelator by employing antenna arrays and the gain increases as the number of antennas increases and the angle dispersion decreases. It is also shown that we can increase the asymptotic efficiency of the decorrelating detector with base-station antenna arrays up to unity if we use an infinite number of antennas when the channel is angle-nondispersive: we cannot, however, increase the asymptotic efficiency of the decorrelating detector by employing base-station antenna arrays if the dispersion is infinite.