Lyapunov Optimization-Based Latency-Bounded Allocation Using Deep Deterministic Policy Gradient for 11ax Spatial Reuse

IEEE 802.11ax introduces Uplink Orthogonal Frequency Division Multiple Access (OFDMA)-based Random Access (UORA), a novel feature for facilitating random channel access in Wireless Local Area Networks (WLANs). Similar to the conventional random access scheme in WLANs, UORA employs the OFDMA backoff (OBO) procedure to access the channel’s Resource Units (RUs) and selects a random OBO counter within the OFDMA contention window (OCW) range. The Access Point (AP) can determine and communicate this OCW range to each station (STA). Multiple STAs accessing RUs result in transmission failure due to RU collisions, which occur when specific RUs remain unassessed by any STA, leading to wastage. Efforts to optimize channel efficiency require minimizing both collisions and idle RU despite the challenges arising from UORA’s distributed and random nature. The Fisher-Yates shuffle algorithm introduces a random uniform distribution strategy for managing RU allocations among STAs. The results demonstrate that this approach enables STAs to access RUs in a distributed manner, effectively reducing idle and wasted RUs, especially in scenarios involving a limited number of STAs. Furthermore, this approach effectively mitigates collisions among STAs, even in scenarios with a more significant number of STAs.

This paper addresses the orthogonal frequency-division multiple access (OFDMA) resource allocation and wavelength assignment problems in wavelength-division multiplexing (WDM) radio-over-fiber picocellular networks with OFDMA as the wireless modulation and access scheme. We consider the case that the number of WDM wavelengths is limited in which one wavelength is shared among multiple picocells. The set of picocells sharing the same wavelength is referred to as a nanocell in this paper. Since picocells in the same nanocell cannot be allocated with OFDMA resource block (RB) of the same frequency at a time, the intra-nanocell interference is eliminated. However, picocells in different nanocells may be allocated with OFDMA RBs of the same frequency at a time, thus posing interference to each other. To minimize the inter-nanocell interference, OFDMA RBs of the same frequency are assigned to picocells which pose the least interference to each other. However, this may result in some picocells being allocated with a large number of OFDMA RBs, leading to the limited power share received by each OFDMA RB because of the power constraint of the picocell. To minimize the inter-nanocell interference with consideration of the power constraints of picocells, we recast the OFDMA resource allocation and wavelength assignment problems into graph problems, and then propose corresponding solutions.

The next generation wireless local area network (WLAN) needs to significantly improve the area throughput in high-dense deployment scenario. Orthogonal frequency division multiple access (OFDMA), considered as the key technology of the next generation WLAN, has been adopted by IEEE 802.11ax. However, most existing studies have one tricky problem: interference extension problem, i.e., the stations (STAs) placed at dispersive locations from one basic service set (BSS) access channel and transmit data simultaneously through OFDMA, thereby interfering a large area and suppressing the potential transmissions around this BSS. Unfortunately, high-dense deployment scenario exacerbates interference extension problem. This article proposes a spatial clustering group division-based OFDMA (SCGD-OFDMA) protocol, which enables the geographically close STAs to form spatial clustering groups, named SCGs. Each SCG has a leader STA and several member STAs. Each SCG’s leader STA contends for channel resources. After that, the leader STAs that successfully contending channel are scheduled by the access point one by one to trigger its member STAs to transmit uplink data by using OFDMA. Therefore, the geographical interference area is reduced and the area throughput is improved since the concurrent STAs in one SCG are located in limited area. This article theoretically analyzes the optimal SCG establishment, and throughput and area throughput of SCGD-OFDMA. Theoretical analysis is consistent with simulation results. The simulation results also show that when the number of STAs is 200 and all resource units are used for random access, SCGD-OFDMA outperforms IEEE 802.11ax and OMAX in area throughput by 56.13% and 190.97%, respectively.

IEEE 802.11ax uplink orthogonal frequency division multiple access (OFDMA)-based random access (UORA) is a new feature for random channel access in wireless local area networks (WLANs). Similar to the legacy random access scheme in WLANs, UORA performs the OFDMA backoff (OBO) procedure to access the channel and decides on a random OBO counter within the OFDMA contention window (OCW) value. An access point (AP) can determine the OCW range and inform each station (STA) of it. However, how to determine a reasonable OCW range is beyond the scope of the IEEE 802.11ax standard. The OCW range is crucial to the UORA performance, and it primarily depends on the number of contending STAs, but it is challenging for the AP to accurately and quickly estimate or keep track of the number of contending STAs without the aid of a specific signaling mechanism. In addition, the one for this purpose incurs an additional delay and overhead in the channel access procedure. Therefore, the performance of a UORA scheme can be degraded by an improper OCW range, especially when the number of contending STAs changes dynamically. We first observed the effect of OCW values on channel efficiency and derived its optimal value from an analytical model. Next, we proposed a simple yet effective OBO control scheme where each STA determines its own OBO counter in a distributed manner rather than adjusting the OCW value globally. In the proposed scheme, each STA determines an appropriate OBO counter depending on whether the previous transmission was successful or not so that collisions can be mitigated without leaving OFDMA resource units unnecessarily idle. The results of a simulation study confirm that the throughput of the proposed scheme is comparable to the optimal OCW-based scheme and is improved by up to 15 times compared to the standard UORA scheme.

The design of a dual-band circularly polarized wearable textile antenna is presented. The antenna consists of a slotted split-ring textile patch with a full ground plane. It features a 46 × 46 mm2 square patch over 70 × 70 mm2 ground plane using a 3-mm felt substrate. The proposed square radiator is modified using slotted split-ring to cater for dual-band resonance. The antenna is capable of providing dual-band coverage for the entire 1.8 and 2.6 GHz for the Fourth-Generation (4G) Long-Term Evolution (LTE), and for the 2.45-GHz Wireless Local Area Network (WLAN) applications. The antenna featured an impedance bandwidth of 70 MHz (1.76–1.83 GHz) in the 4G LTE (Band 3) and 400 MHz (2.36–2.76 GHz) in the Industrial, Medical and Scientific (ISM) band. The measured 3-dB axial-ratio bandwidths are 2.8% (in the lower band) and 4.2% (in the upper band) with a maximum realized gain of 3.2 dB at 2.45 GHz. Simulations and measurements indicated a good agreement with suitability to be applied in the 4G and WLAN bands.

We present a monolithically integrated optical receiver fabricated with standard silicon processing technology for fiber-wireless IEEE 802.11 wireless local area network (WLAN) applications. The receiver contains a silicon avalanche photodetector and a transimpedance amplifier and has up to 5.6-GHz photodetection bandwidth. Using this integrated optical receiver, transmission of 54-Mb/s WLAN signals at 2.4-GHz and 5-GHz bands is successfully achieved with 2.6-% and 3.0-% error vector magnitude, respectively.

This paper presents the development of dual-band patch antenna incorporated with split ring resonator (SRR) for Global Positioning System (GPS) and Wireless Local Area Network (WLAN) application. The antenna is composed of 3 layers of copper conductor flanking 2 layers of FR4 Epoxy dielectric substrate with the total thickness of 1.6mm and the dimension of 78.6mm × 48.4mm. The characterization shows that the resonant frequency of first frequency band is 1.47GHz with reflection coefficient of −16.4dB and −10dB working bandwidth of 335MHz. Whilst the resonant frequency of second frequency band is 2.43GHz with reflection coefficient of −22.6dB and −10dB working bandwidth of 60MHz.

This research presents the design and implementation of a dual-band patch antenna (DBPA) optimized for 2.4 GHz and 5 GHz wireless local area network (WLAN) applications. The antenna features a modified rectangular patch with a cut corner and two parasitic rectangular patches, enabling dual-band operation with enhanced gain. The DBPA is fed by a 50-Ohm coplanar waveguide and fabricated on a single-layer copper circuit board using a flame-retardant 4 substrate with a relative permittivity of 4.3 and a thickness of 1.6 mm. A prototype with compact dimensions of 0.040×0.040×0.0009 λ³ was constructed and experimentally evaluated. Measurements reveal a nearly omnidirectional radiation pattern, achieving peak gains of 2.92 dBi at 2.4 GHz and 4.25 dBi at 5 GHz. The antenna demonstrates a wide 10 dB return loss bandwidth of 67.7% (1.7–3.44 GHz) for the lower band and 56% (4.59–8.16 GHz) for the upper band. The strong agreement between simulated and measured results validates the design’s potential for practical and scalable implementation. This DBPA design offers a simpler, more compact, and wider-bandwidth alternative to conventional antennas, making it ideal for modern WLAN systems.

This paper proposes a reinforcement learning (RL) algorithm for the security problem of state estimation of cyber-physical system (CPS) under denial-of-service (DoS) attacks. The security of CPS will inevitably decline when faced with malicious cyber attacks. In order to analyze the impact of cyber attacks on CPS performance, a Kalman filter, as an adaptive state estimation technology, is combined with an RL method to evaluate the issue of system security, where estimation performance is adopted as an evaluation criterion. Then, the transition of estimation error covariance under a DoS attack is described as a Markov decision process, and the RL algorithm could be applied to resolve the optimal countermeasures. Meanwhile, the interactive combat between defender and attacker could be regarded as a two-player zero-sum game, where the Nash equilibrium policy exists but needs to be solved. Considering the energy constraints, the action selection of both sides will be restricted by setting certain cost functions. The proposed RL approach is designed from three different perspectives, including the defender, the attacker and the interactive game of two opposite sides. In addition, the framework of Q-learning and state–action–reward–state–action (SARSA) methods are investigated separately in this paper to analyze the influence of different RL algorithms. The results show that both algorithms obtain the corresponding optimal policy and the Nash equilibrium policy of the zero-sum interactive game. Through comparative analysis of two algorithms, it is verified that the differences between Q-Learning and SARSA could be applied effectively into the secure state estimation in CPS.

In this paper we present a two-dimensional medium access control (MAC) protocol. Orthogonal frequency division multiple access (OFDMA) can make multiple stations (STA) transmit simultaneously on different sub-channels. On the other hand, carrier sense multiple access with collision avoidance (CSMA/CA) could make different stations contend the available channel from the time domain to avoid collision with each other. We propose a two-dimensional MAC protocol based on OFDMA and CSMA/CA in broadband systems. With the new designed MAC protocol different stations will access the channel from the time-frequency domain without interference and collision. The combination of OFDMA with CSMA/CA will improve the system throughput with efficient MAC and decrease the collision probability. We design that different stations will contend the available time-frequency resources dynamically under fairness. The system throughput of the designed protocol is analyzed and simulation results are presented to show the performance under our designed protocol far better than the conventional CSMA/CA protocol.

This paper presents the design of a compact miniaturized indented T shaped Monopole antenna for Wireless Local Area Network (WLAN) applications covering the 5.15-5.35 GHz band. The proposed antenna is a center offset indented T with a compact size of 13 mm by 20 mm and 0.8 mm thick, low profile enough for integration with Monolithic Microwave Integrated Circuit (MMIC). Design and simulation was carried out using High Frequency Structure Simulator (HFSS) from Ansoft, a commercial software and the results obtained shows a return loss (RL) better than 10dB at 41dB within the impedance bandwidth of 4.83-5.70 GHz at a central frequency of 5.2 GHz with a stable omnidirectional radiation pattern with a total Gain of 2.5 dBi which is suitable for compact space WLAN applications.

A multi-input multi-output (MIMO) antenna for wireless local area network (WLAN) applications operating in 2.4 GHz and 5.8 GHz frequency bands is proposed in this paper. The proposed dual-band MIMO antenna is composed of two symmetrical radiation elements, and the isolation performance is improved by adopting parasitic elements and a defective ground plane. The measured reflection coefficients are less than −10 dB in the bandwidth range of 2.12–2.8 GHz and 4.95–6.65 GHz, respectively. The measurements show excellent isolation of −21 dB and −15 dB in both desired frequency bands, respectively. The total peak gain is greater than 4.8 dBi. The calculated envelope correlation coefficients (ECC), based on the measured S-parameters, are smaller than 0.01 and 0.024 in the lower and higher frequency bands, respectively. The dimension of the presented antenna occupies 50 × 40 × 1.59 mm3. It is suitable for IEEE 802.11 a/b/g/n (2.4–2.4835 GHz, 5.15–5.35 GHz and 5.725–5.85 GHz) WLAN applications.

In complex urban wireless environments, unmanned aerial vehicle–mobile edge computing (UAV-MEC) systems face challenges like link blockage and single-antenna eavesdropping threats. The traditional single reconfigurable intelligent surface (RIS), limited in collaboration, struggles to address these issues. This paper proposes a double-RIS cooperative UAV-MEC optimization scheme, leveraging their joint reflection to build multi-dimensional signal paths, boosting legitimate link gains while suppressing eavesdropping channels. It considers double-RIS phase shifts, ground user (GU) transmission power, UAV trajectories, resource allocation, and receiving beamforming, aiming to maximize secure energy efficiency (EE) while ensuring long-term stability of GU and UAV task queues. Given random task arrivals and high-dimensional variable coupling, a dynamic model integrating queue stability and secure transmission constraints is built using Lyapunov optimization, transforming long-term stochastic optimization into slot-by-slot deterministic decisions via the drift-plus-penalty method. To handle high-dimensional continuous spaces, an end-to-end proximal policy optimization (PPO) framework is designed for online learning of multi-dimensional resource allocation and direct acquisition of joint optimization strategies. Simulation results show that compared with benchmark schemes (e.g., single RIS, non-cooperative double RIS) and reinforcement learning algorithms (e.g., advantage actor–critic (A2C), deep deterministic policy gradient (DDPG), deep Q-network (DQN)), the proposed scheme achieves significant improvements in secure EE and queue stability, with faster convergence and better optimization effects, fully verifying its superiority and robustness in complex scenarios.

The long term evolution (LTE) system employs orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) for the downlink and uplink transmission, respectively. However, in most existing literatures regarding the two-way OFDMA resource allocation, all terminals are assumed under an OFDMA operation, and the allocation scheme is always considered solely under the frequency domain for subcarrier assignment. In this letter, a joint time and frequency resource allocation algorithm for the LTE two-way relaying is proposed, in which the permutation of the subframe and the resource block is discussed for augmenting the system capacity.

IEEE 802.16 standard and its marketing technology Worldwide Interoperability for Microwave Access (WiMAX) is one of the leading technology that gain benefit of adopting orthogonal frequency division multiple access (OFDMA) as its multiple access technique. OFDMA gives flexibility in resources allocation to accommodate a large number of users supporting several services classes with quality of service (QoS). This loads big challenges on its resource allocation. One of the key performance factors of OFDMA resource allocation is its downlink data packing mechanism. In IEEE802.16 standard based OFDMA the downlink data is packed into down link frames in the form of rectangular slots called burst. The standard leaves details of packing mechanism as an open issue for researchers and manufacturer to implement. Therefore recently several algorithms have been proposed in literature. This paper endeavours to identify key factors and tradeoffs issues associated with designing of downlink data packing algorithm for WiMAX based IEEE802.16 through a competitive survey of recent proposed algorithms.