Wi-Fi Coexistence Research Articles

Distributed DQN-based network-wide energy efficiency maximization for 5G NR-U and Wi-Fi coexistence environments

To effectively manage the escalating traffic, attention is drawn to the coexistence mechanism of cellular and Wi-Fi networks which offload the cellular traffic from the licensed band to the unlicensed band. For the coexistence of 5G new radio-unlicensed and Wi-Fi, we tackle the energy efficiency maximization problem by sequentially determining the duty cycle and transmit power through the use of distributed deep Q-network (DQN) techniques. When utilizing the existing unlicensed band, the proposed method minimizes the impact on Wi-Fi networks while achieving optimal energy efficiency. Simulations validate the superior energy efficiency of the proposed coexistence mechanism over various benchmark methods.

Proportional Fairness for Long-Term Evolution-Licensed Assisted Access (LTE-LAA) with Wi-Fi Coexistence in Unlicensed Spectrum

Long-Term Evaluation-Licensed Assisted Access (LTE-LAA) has good potential for fair coexistence with Wi-Fi in an unlicensed spectrum. Though the LTE-LAA utilizes the same listen before-talk technique as the distributed coordination function in IEEE 802.11, it utilizes completely different parameters and transmission durations. For this reason, a fair coexistence between LTE-LAA and Wi-Fi leaves an open question on how the LTE-LAA network should choose its parameters. To tackle this issue, an analytical framework considering the effects of varying important parameters, which are the different initial back-off window sizes, the numbers of sensing durations, the maximum back-off stages, the number of retransmissions and the transmission opportunities for LTE-LAA and Wi-Fi nodes on their performances has been developed. The node and network airtime performances are evaluated by using the current standard parameters setting to see how this setting affects the node and network airtime performances. From there, optimal settings of the initial backoff window size and number of sensing durations are applied by using the obtained node airtime equation that is derived from the Markov renewal process and evaluated as functions of system parameters. The optimum initial backoff window size and number of sensing durations of LTE-LAA are evaluated and verified by the calculation and simulation using MATLAB software. The analysis shows that LTE-LAA maintained unfair coexistence with Wi-Fi by using the current standard parameter setting as its initial back off window size or sensing duration. But in contrast, using the optimum initial backoff window size and number of sensing durations of LTE-LAA shows that they can maintain proportional fairness. It is unconcealed that the initial backoff window size tuning of LTE-LAA carries a high possibility of achieving fairness because it needs less system data and achieves a higher exactness result.

Exploiting Successive Interference Cancellation for Spectrum Sharing Over Unlicensed Bands

Harmonious coexistence among different unlicensed wireless technologies has became increasingly important due to the spectrum shortage problem. As a representative case, we focus on addressing LTE-LAA and WiFi coexistence in unlicensed bands. Traditionally, collision avoidance-based medium access control (MAC) protocols adopted by both LAA and WiFi have led to low channel utilization and fairness. In this paper, we explore physical-layer interference suppression techniques (e.g., successive interference cancellation, SIC) to enhance the spectrum utilization of coexisting LAA and WiFi networks. We propose a SIC-aware MAC protocol that embraces concurrent transmissions and optimizes the channel access strategy at the MAC layer, so as to mitigate the interference (same-technology or cross-technology) due to excess channel contentions. We theoretically analyze the network throughput by extending Bianchi's Markov model, considering the impact of concurrent transmissions and SIC. We also extend the analysis to consider MIMO and MU-MIMO links with SIC. We validate our theoretical analysis and the effectiveness of the proposed MAC protocol via extensive simulations. We also implement a prototype LAA/WiFi SIC receiver on USRP devices to demonstrate the feasibility of cross-technology SIC and the proposed MAC protocol.

Fair and Secure 5G and Wi-Fi Coexistence Using Robust Implicit Channel Coordination

Fair and Secure 5G and Wi-Fi Coexistence Using Robust Implicit Channel Coordination

Coexistence of Hybrid VLC-RF and Wi-Fi for Indoor Wireless Communication Systems: An Intelligent Approach

Coexistence of Hybrid VLC-RF and Wi-Fi for Indoor Wireless Communication Systems: An Intelligent Approach

Performance Modeling of an NR-U and WiFi Coexistence System Using the NR-U Category-4 LBT Procedure and WiFi DCF Mechanism in the Presence of Hidden Nodes

The hidden-node problem is an important problem that should be considered in the design of a wireless communication system. This paper studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U category-4 LBT procedure and WiFi DCF mechanism in the presence of hidden nodes. 2-D Markov models are first developed to describe the NR-U category-4 LBT procedure of an NR-U gNB and the WiFi DCF procedure of a WiFi AP, respectively, taking into account the effects of hidden nodes. Based on the two Markov models, theoretical models are further derived for analyzing the throughput of a gNB/AP and the delay of an NR-U/WiFi packet. Finally, the derived theoretical models are validated through simulation results and based on the theoretical models, the impacts of major system parameters on the system performance in terms of the throughput and packet delay are investigated, including the data packet arrival rate, the density, the sensing distance, and the channel transmission rate of a gNB.

Performance Modeling of an NR-U and WiFi Coexistence System Using the NR-U Category-4 LBT Procedure and 802.11e EDCA Mechanism in the Presence of Hidden Nodes

This paper studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U category-4 LBT procedure and 802.11e EDCA mechanism in the presence of hidden nodes. 3-D Markov models are first developed to describe the NR-U category-4 LBT procedure for a priority-p queue of an NR-U gNB and the 802.11e EDCA mechanism for an AC-q queue of a WiFi AP, taking into account the effects of hidden nodes and the transmission of different-priority data. Based on the Markov models, theoretical models are derived for analyzing the mean throughput of a priority-p queue in an NR-U gNB and that of an AC-q queue in a WiFi AP as well as the mean transmission delay of an NR-U priority-p data packet and that of a WiFi AC-q data packet. The derived theoretical performance models are validated through simulation results. Based on the performance models, the impacts of major system parameters on the system performance are investigated, including the density of NR-U gNBs, the sensing distance and channel transmission rate of an NR-U gNB, and the data packet arrival rate at an NR-U gNB.

RIS Aided NR-U and Wi-Fi Coexistence in Single Cell and Multiple Cell Networks on Unlicensed Bands

To address the scarcity of spectrum resource incurred by explosively increasing traffic load in existing fifth generation (5G) networks, we consider exploiting Reconfigurable intelligent surface (RIS) to harmonize the coexistence of cellular networks and WiFi system on the unlicensed bands. In particular, RIS is capable of not only improving the performance of new radio on unlicensed bands (NR-U) by increasing the signal to interference and noise ratio (SINR) of cellular users, but also decreasing the interference to the existing WiFi system caused by NR-U. Thus, we investigate the performance of RIS aided coexisting networks both in single cell and multiple cell scenarios. For the single cell scenario, we aim to improve the worst transmission rate of UEs in NR-U network. The problem is solved by a proposed alternating optimization-based solution. For the multiple cell scenario, cell cooperation is exploited jointly with multiple RISs to maximize the sum-rate of all UEs. Although the problem is more challenging than that of single cell case, we propose a multi-agent reinforcement learning (MARL) algorithm to solve it. Numeral results verify the effectiveness of our proposed schemes and show that deploying RISs is a promising solution for the enhancement of NR-U networks.

Channel Access Optimization in Unlicensed Spectrum for Downlink URLLC: Centralized and Federated DRL Approaches

The sixth-generation (6G) communication research is currently in the early stage, where ultra-reliable low-latency communication (URLLC) is still an important service as in the fifth-generation (5G). Since 6G networks are expected to provide even higher levels of massive connectivity, high spectrum efficiency, high reliability, and low latency than 5G communication, it would confront much more severe spectrum scarcity problems, which make the new radio in unlicensed spectrum (NR-U) technology attractive. However, how to achieve URLLC requirements in NR-U networks is extremely challenging due to interference and collisions among multiple radio access technologies (e.g., WiFi). Therefore, it is urgent to design efficient spectrum-sharing algorithms to support URLLC in emerging 6G networks. In this paper, we develop novel centralized deep reinforcement learning (CDRL) and federated DRL (FDRL) frameworks, respectively, to optimize the downlink URLLC transmission in NR-U and WiFi coexistence systems through dynamically adjusting energy detection (ED) thresholds. Our results show that both CDRL and FDRL approaches have improved the reliability of the NR-U system significantly, but the CDRL framework has sacrificed the reliability of the WiFi system. To guarantee the reliability of the WiFi system while improving the NR-U system, we take fairness into account by redesigning the reward of CDRL.

Performance Modeling of an NR-U and WiFi Coexistence System With NR-U Type B Multichannel Access Procedure

New radio-based access to unlicensed bands (NR-U) multichannel access procedures are 3GPP standards for supporting 5G NR-U and WiFi coexistence in unlicensed frequency bands. NR-U provides a new solution to alleviating the severe spectrum scarcity problem of 5G cellular networks in licensed frequency bands for supporting diverse Internet of Things (IoT) services. This article studies the performance modeling of an NR-U and WiFi coexistence system using the NR-U Type B multichannel access procedure and the WiFi DCF procedure and focuses on a system model with two unlicensed channels: 1) a primary channel and 2) a secondary channel. 2-D Markov models are first built to describe the NR-U category-4 LBT procedure and the WiFi DCF procedure on the primary channel, respectively. A 3-D Markov model is then built to describe the WiFi DCF procedure on the secondary channel, taking into account the effect of the NR-U Type B multichannel access procedure. Based on the built Markov models, performance models are further derived for analyzing the system performances in terms of system throughput and packet delay on the primary channel and/or secondary channel. The derived performance models are validated through simulation results. The impacts of the number of NR-U gNBs/WiFi APs and major system parameters on the system performances are investigated based on the derived performance models.

A Game-Theoretic Framework for Coexistence of WiFi and Cellular Networks in the 6-GHz Unlicensed Spectrum

The recently unlocked 6-GHz spectrum is accessible to cellular and WiFi networks for unlicensed use while they conform to the constraints imposed by the incumbent nodes. We allow only a fraction of the cellular base stations (BSs) and a fraction of WiFi access points (APs) to use the 6-GHz band so that sources of interference are spatially segregated and made sparse, thereby decreasing the overall interference to each other. Through our proposed framework, we control this fraction as we group portions of cellular and WiFi network elements into entities competing with the other entities for the spectrum resources. These entities interact to satisfy their Quality of Service demands by playing a non-cooperative game. The action of an entity corresponds to the fraction of its network elements (WiFi APs and cellular BSs) operating in the 6-GHz band. We use tools from stochastic geometry to derive the theoretical performance metrics for users of each radio access technology, which helps us capture the aggregate behaviour of the network in a snapshot. Due to the decentralized nature of the game, we find the solution using distributed Best Response Algorithm ( <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D-BRA</monospace> ), which improves the average datarate by 11.37% and 18.59% for cellular and WiFi networks, respectively, with random strategy as the baseline. The results demonstrate how the system parameters affect the performance of a network at equilibrium and highlight the throughput gains of the networks as a result of using the 6-GHz bands, which offer considerably larger bandwidths. We tested our framework using real-world data, which shows that practical implementation of multi-entity spectrum sharing is feasible even when the spatial distribution of the network elements and population are non-homogeneous.

A new fair-efficient spectrum allocation scheme for the LTE and WiFi coexistence platform

Long-term evolution (LTE) carrier aggregation with the unlicensed WiFi spectrum band has been pointed out as a good solution to handle the rapidly increasing wireless data traffic amounts. With both LTE and WiFi networks, the investigation of their coexistence is a hot research topic of active interest, primarily driven by industry and academia. In this study, we investigate a new spectrum allocation scheme for the LTE/WiFi coexistence platform. To maximize the system throughput while guaranteeing a relative fairness between heterogeneous networks, we adopt the cooperative game paradigm to design our novel scheme. According to the basic ideas of Proportional Nash bargaining solution (PNBS) and Zhang’s group bargaining solution (ZGBS), we can leverage a mutual consensus to provide a fair-efficient solution for the LTE/WiFi spectrum sharing problem. Based on the online interactive bargaining approach, network agents work together to effectively share the LTE and WiFi spectrum resources. Under dynamically changing network environments, it is an essential approach to find the relevant trade-off between conflicting requirements, i.e., fairness and efficiency. Validated by simulation results, our proposed scheme can provide important insights into the LTE/WiFi system operations. Finally, we forecast further research trends on the basis of our conclusion.

Impact of hidden node problem in association and data transmission for LAA Wi-Fi coexistence

Small-cell LTE and Wi-Fi networks has been globally deployed in the unlicensed 5 GHz bands, leading to the need for new coexistence regulations between two very different access technologies. To address coexistence challenges, 3GPP standardized LTE Licensed Assisted Access (LAA) in 5 GHz bands through the incorporation of similar sensing and back-off features. The success of LAA’s fair and efficient coexistence with Wi-Fi can be considered a benchmark for collaborative cellular operation in unlicensed bands. In this paper, we discuss the hidden node scenario when T-Mobile LAA coexists with the Wi-Fi APs that we deployed at the Illinois Institute of Technology (IIT) university campus. In this setup, we observed problems on the Wi-Fi client association and inefficient data transmission when it tries to connect to its corresponding Wi-Fi APs. As LAA is unaware of the Wi-Fi AP’s transmission (low transmission power received at LAA BS), LAA BS continuously transmits with maximum transmission opportunity time, thus highly impacting Wi-Fi performance. Further, the hidden node problem is modeled analytically capturing the root cause of inefficiency.

Unlicensed Spectrum Allocation for LTE and Wi-Fi Coexistence with HAP

In order to accommodate the ever-increasing traffic demands, numerous approaches have been developed to improve spectrum utilization. Among others, the coexistence of LTE (Long-Term Evolution) and Wi-Fi, addressed by the 3GPP (3rd Generation Partnership Project) with hyper access points (HAPs) as bridges, is well recognized as a promising candidate solution. Aimed at improving the spectrum utilization of the unlicensed bands by following LTE-Unlicensed (LTE-U), this article contributes to the determination of the optimal time ratio, δ, for the time-division multiplexing of LTE and Wi-Fi over unlicensed bands. Symmetric allocation with a duty cycle of 50% cannot be an optimal option. Asymmetric allocation according to the quality of service (QoS) requirements and traffic demands should be considered. The problem is formulated as an optimization problem optimizing the total throughput. The lower and upper bounds of δ are obtained according to the QoS requirements of Wi-Fi and the admission control requirements of LTE. The detailed procedure for finding an adequate δ is developed and presented. A series of simulations are conducted to demonstrate the feasibility and effectiveness of the proposed approach. Simulation results show that the proposed approach improves the total throughput without compromising the fairness of Wi-Fi, as intended. Ten percent of improvement in throughput compared with LTE-U can be achieved.

Design and Implementation of an IoT Gateway for Zigbee and WiFi

This paper proposed a framework called IAPA (Integrated Access Point Architecture) that applied an off-the-shelf AP (Access Point) device on WLAN (Wireless Local Area Network) as an IoT (Internet-of-Things) gateway to integrate Zigbee and Wifi. This Wifi-Zigbee AP (called WiZAP) has the advantages of low cost, small size and low power consumption. However, the coexistence of Wifi and Zigbee in unlicensed bands will introduce a serious data collision problem. In this paper, we propose a linear-time balance-first configuration strategy to adjust Wifi parameters to reduce data collision. A strategy to dynamically configure these parameters for MAC layer communication is also proposed. Experiments test the influence of network transmission in real application scenarios. Results show that our WiZAP can work efficiently with the coexistence of Wifi and Zigbee.

On the Effects of Transmit Power Control on Multi Carrier LAA-WiFi Coexistence

To meet the ever increasing data rate demand in cellular network, the 3rd Generation Partnership Project (3GPP) introduced Licensed Assisted Access (LAA) with Listen Before Talk (LBT) mechanism to utilize the unlicensed spectrum to supplement the licensed LTE users. However, this leads to interference to already incumbent technologies in unlicensed spectrum such as WiFi. Furthermore, multi-carrier aggregation has been proposed to further increase the capacity in unlicensed spectrum. As WiFi primarily works on the principle of energy detection in the channel, in this paper, we first develop an analytical model to measure the performance of LAA and WiFi coexistence in unlicensed spectrum which supports multi-carrier aggregation which employs SINR based collision that allows the possibility of concurrent transmissions. Further, to reduce the interference to WiFi, we propose a coexistence method named Carrier Aggregation with Transmit Power Control (CATPC) which dynamically adjusts the LAA transmit power. CATPC provides a better opportunity for WiFi devices, better channel utilization, and energy efficient transmission by LAA. Through extensive simulations we demonstrate the effectiveness of CATPC when compared to other coexistence methods proposed in the literature.

BCSM: Blockchain‐based cooperative spectrum management system for 5G NR‐U and WiFi coexistence in the unlicensed band

The licensed band is crowded and suffers from immense mobile data traffic growth, which exceeded 58 exabytes per month in 5 years. Meanwhile, a significant portion of the unlicensed band is underutilized and not coordinated efficiently. Experiments in some urban areas of the world have shown that only 5% of the unlicensed 5 GHz band is being used. 5G NR-U technology supports 5G networks in the unlicensed band to alleviate the traffic congestion and boosts 5G networks capacity. Different heterogeneous network access technologies already use the unlicensed band. Consequently, 5G NR-U networks will operate in the proximity of the other coexisting networks, such as WiFi networks in the 5 GHz and 6 GHz bands. In such environments, assessing the shared spectrum becomes challenging and necessitates adequate protocols to identify idle slots for successful transmissions. Cooperative Spectrum Sensing (CSS) improves the spectrum assessment process, as the decision about the spectrum state is rendered based on the local decisions of multiple sensing nodes. CSS is exploited by integrating it with Blockchain technology to design a decentralized cooperative spectrum management system called: Blockchain-Based Cooperative Spectrum Management (BCSM). The system is attributed to ameliorating 5G NR-U awareness about the neighboring WiFi networks traffic in the unlicensed band. An algorithm is designed for performing distributed cooperative spectrum assessment between the 5G NR-U base stations to profile the WiFi networks traffic in their proximity. To ensure fairness based on the effort expended in assessing the spectrum, a priority-based algorithm is designed for spectrum access scheduling. A proof-of-concept is implemented using private Ethereum Blockchain and NS3 simulator. Finally, the system's accuracy is evaluated empirically along with theoretical security analysis.

Joint Subchannel Allocation and Power Control in Licensed and Unlicensed Spectrum for Multi-Cell UAV-Cellular Network

In this paper, we investigate the resource and interference management problem in a novel scenario where multiple unmanned aerial vehicle base stations (UAV-BSs) provide cellular services to UAV users (UAV-UEs) by reusing both licensed and unlicensed spectrum. Considering the co-existence of terrestrial cellular, WiFi and UAV-BSs, a joint optimization problem is formulated for both subchannel allocation and power control of UAV-UEs over the licensed/unlicensed spectrum in order to maximize the uplink sum-rate of the multi-cell UAV-cellular network. Since the formulated problem is NP-hard, we decompose it into three sub-problems. Specifically, we first use the convex optimization and the Hungarian algorithm to obtain the global optimal of power and subchannel allocations in the licensed spectrum, respectively. Then, we propose a matching game with externalities and coalition game algorithms to obtain the Nash stable of the subchannel allocation in the unlicensed band. Local optimal power assignment in the unlicensed spectrum is obtained using the successive convex approximation (SCA) method. An iterative algorithm is thereby developed to solve the three sub-problems sequentially till reaching convergence. Simulation results show that the proposed algorithm can improve the network capacity by nearly two times than the Long Term Evolution-Advanced (LTE-A).

Performance Analysis of an LAA and WiFi Coexistence System Using the LAA Category-4 LBT Procedure With GAP

LTE LAA listen-before-talk (LBT) procedures have been considered a promising solution to reasonable coexistence of LTE with other access technologies in unlicensed spectrum. An issue that arises with the LAA LBT procedures is the so-called GAP period, which may largely degrade the performance of a coexistence system. There are two methods to deal with the GAP period. Method 1 is to fill in the channel during a GAP period by using a reservation signal, while Method 2 takes no action but just listens to the channel during a GAP period. Most existing analytical models for the LAA LBT procedures are inaccurate because they do not take into account the GAP period. This paper studies the modeling of the LAA category-4 LBT procedure in an LAA and WiFi coexistence system and investigate the impact of the GAP period on the system performance. A 2-D Markov chain is built to model the category-4 LBT procedure of an LAA eNodeB, considering the effect of the GAP period. Based the Markov model, analytical models are further derived to investigate the throughput and packet delay performance of the coexistence system with Method 1 and Method 2, respectively. Numerical results show that with Method 1, the performance of an LAA eNodeB is similar to that of a WiFi AP in terms of the transmission probability and packet delay. With Method 2, the performance of an LAA eNodeB is worse than that of a WiFi AP.

Joint Time and Power Allocation for 5G NR Unlicensed Systems

The fifth-generation (5G) and beyond networks are designed to efficiently utilize the spectrum resources to meet various quality of service (QoS) requirements. The unlicensed frequency bands used by WiFi are mainly deployed for indoor applications and are not always fully occupied. The cellular industry has been working to enable cellular and WiFi coexistence. In particular, 5G New Radio in unlicensed channel spectrum (NR-U) supports the uplink and downlink transmission on the maximum channel occupation time (MCOT) duration. In this paper, we consider maximizing the total throughput of both downlink and uplink in NR-U by jointly optimizing the time and power allocation during MCOT while ensuring fair coexistence with WiFi. Fairness is guaranteed in two steps: 1) tuning the access related parameters of NR-U to achieve proportional fairness, and 2) including 3GPP fairness from the throughput perspective as a constraint in NR-U throughput maximization. Numerical analysis and simulation have demonstrated the superior performance of the proposed resource allocation algorithm compared to conventional deployment strategies.