Channel Access Scheme Research Articles

Channel Access Scheme With Alignment Reference Interval Adaptation (ARIA) for Frequency Reuse in Unlicensed Band LTE: Fuzzy Q-Learning Approach

In licensed-assisted access using the LTE (LAA) standard, carrier sensing via the listen-before-talk (LBT) procedure is a vital feature for fair sharing with the Wi-Fi systems. Furthermore, it has been designed to support frequency reuse-1 operation among all cells by the virtue of licensed spectrum. As opposed to the two existing channel-access schemes for frequency reuse-1, transmission start time alignment (TSTA) and energy detection threshold adaptation (EDTA), which may not be able to maximize the LAA system throughput without violating the requirement of fair coexistence, we propose a new frequency-reuse-1 scheme, referred to as the alignment reference interval adaptation-based LAA (ARIA-LAA). It attempts to combine the advantages of TSTA and EDTA into a unified access framework, in which the alignment reference interval (ARI) is adaptively adjusted to control the channel-access probability for LAA and Wi-Fi systems. Meanwhile, to operate the ARIA-LAA effectively toward our design objective, we design the fuzzy Q-learning system that adapts the continuous variable ARI to the dynamically changing wireless network environment. Based on the analytical system models and formation of the optimization problem, it employs a model-free learning algorithm that interacts with the state, defined as the current level of fairness achieved by adaptation, and the Q-learning function to determine the ARI as a global action. Our simulation results demonstrate that the ARIA-LAA is a novel scheme of spectrum sharing with spatial reuse for LAA that enhances the overall system capacity while satisfying the fair-coexistence requirement in the unlicensed spectrum.

An Adaptive Multi-Channel Assignment and Coordination Scheme for IEEE 802.11P/1609.4 in Vehicular Ad-Hoc Networks

Vehicular ad-hoc networks (VANETs) have been developed to provide safety-related and commercial service applications on the road. The IEEE 1609.4 is a standard (legacy) designed to support multi-channels in VANETs, namely control channel (CCH) and service channels (SCHs) with fixed alternating CCH and SCH intervals. The CCH is dedicated to broadcast safety and control applications while SCHs are used to transfer service data applications. However, due to the nature of contention-based channel access scheme and the transmission of multiple applications over the CCH during a fixed interval, safety applications performance is degraded during CCH congestion in high network density scenarios. In this paper, we propose an adaptive multi-channel assignment and coordination (AMAC) scheme for the IEEE 802.11p/1609.4 in VANETs which exploits channel access scheduling and channel switching in a novel way. AMAC scheme includes an adaptive execution of the peer-to-peer negotiation phase between service providers and users for SCH resource reservations, and collision-aware packet transmission mechanisms. These two mechanisms alleviate collisions and increase packet delivery ratio (PDR) of safety applications on the CCH. Thereby, the AMAC scheme ensures an efficient and reliable quality of service (QoS) for different traffic flows and improves the time diversity among vehicles based on the traffic conditions. For performance analysis, analytical models are developed based on 1-D and 2-D Markov chain models taking into account an error-prone channels. The probabilities of successful transmission and collisions have been derived to compute PDR, and delay for safety packets in legacy standard and AMAC scheme. Analytical and simulation results indicate that the AMAC scheme reduces the collisions and increases the PDR for safety applications over the CCH compared with the legacy standard. In addition, AMAC scheme outperforms the legacy standard in terms of system throughput of service applications.

A Hybrid Channel Access Scheme for Coexistence Mitigation in IEEE 802.15.4-Based WBAN

Wireless body area network (WBAN) is a communication technology, which aims providing both medical and consumer electronics services through sensor devices in, on, or around a human body. Due to the absence of the IEEE 802.15.6-based RF modules, the IEEE 802.15.4, a typical low-power communication technology of which requirements are similar, is considered to implement WBANs. In the case where a lot of WBANs coexist, meanwhile, collisions and signal attenuations may lead to their communication performance degradation. However, the IEEE 802.15.4 does not provide any solutions to solve coexistence problems, and thus, coexistence mitigation schemes for the IEEE 802.15.4-based WBANs are necessary. In this paper, we perform preliminary experiments to identify aspects of coexistence problem among the coexisting IEEE 802.15.4-based WBANs. Based on the results of preliminary experiments, we also propose a hybrid channel access scheme to mitigate coexistence problems in WBANs. The proposed scheme can be classified into two phases. In the first phase, the proposed scheme provides probabilistic collision avoidance on the contention-free period. When the pre-defined requirements of reliability cannot be satisfied with performing the first phase, the proposed scheme performs the second phase, which helps to mitigate collision or interference through changing channel access method. To evaluate the performance of the proposed scheme, we implement our scheme and perform experiments by comparing with an IEEE 802.15.4-based WBAN.

Advanced Dynamic Channel Access Strategy in Spectrum Sharing 5G Systems

5G wireless communications aim at providing higher data rates, spectral efficiency, and energy efficiency than 4G. To achieve this target, the spectrum resource with low utilization is emptied out for 5G refarming. The refarmed spectrum is of effective propagation nature; however, it leads to extensive competition between PTOs and DTOs. To mitigate such competition, dynamic spectrum sharing should be realized. For this purpose, a spectrum sharing framework of a 5G system is designed in this article, in which the public users and dedicated users can access the sharing spectrum dynamically. In the framework, to ensure the QoE of the secondary users in a spectrum sharing system, the DTO in this case, an advanced dynamic channel access strategy is proposed. The spectrum sharing system states are modeled as a finite state Markov chain, and are used to analyze the system state transition model. Based on the analysis results, the optimal dynamic channel access strategy with minimum queuing time for DTO is derived by a Markov decision process. Extensive simulations show that the proposed dynamic channel access strategy can achieve the optimal queuing time.

Modelling of synchronisation and energy performance of FBE‐ and LBE‐based standalone LTE‐U networks

Without the aid of licensed channel, deploying long-term evolution (LTE) networks over unlicensed spectrum (named standalone LTE-U networks) faces the difficulty of establishing and maintaining synchronisation between user equipments and base stations. In this work, considering the two modes of listen-before-talk-based channel access scheme, frame-based equipment (FBE) and load-based equipment (LBE), the authors propose analytical frameworks to study the successful probability of synchronisation and the energy consumption of synchronisation in a standalone LTE-U network. Specifically, for the LBE mode, the authors also propose a Lattice-Poisson algorithm-based approach to derive the distribution of the channel non-occupancy period of a standalone LTE-U network. Furthermore, the authors explore the impact of diverse protocol parameters of both FBE and LBE modes on the two studied performance metrics. Simulation results demonstrate the accuracy of the analysis, and shed some light on the selection of FBE and LBE for standalone LTE-U networks, in terms of synchronisation, energy consumption, and throughput of standalone LTE-U and Wi-Fi networks.

Uplink MU‐based channel access scheme for high‐throughput of multiple users

A new channel access scheme to improve the throughput in the medium access control layer is proposed to support the high data rate of multiple users. The proposed scheme is based on access point-coordinated multiuser transmission via the adoption of a trigger frame. The total throughput of the proposed scheme is improved by up to 30% compared with the uplink-multiuser channel access scheme based on the request to send/clear to send exchange. Moreover, as the number of stations increases, the degree of improvement in performance increases.

Delay guaranteed MDP scheduling scheme for HCCA based on 802.11p protocol in V2R environments

SummaryIn recent years, the vehicular ad hoc network has attracted worldwide attention from academe and industry. Many researches have been executed to improve the quality of services (QoS) of the intelligent transportation system. However, current existing channel access schemes at the medium access control layer specified in 802.11 protocol, including hybrid coordination function control channel access (HCCA) and enhanced distributed channel access, could not efficiently achieve the QoS requirements in some special situations. This paper proposes a delay guaranteed HCCA (DG‐HCCA) scheduling scheme, which works based on a Markov decision process model and the measurement of historic performance, to guarantee the QoS enhanced data transmission for vehicles to roadside unit. Besides, this paper also presents a performance analysis model to systematically evaluate the system performance of the channel utility and the average delay. The performance of the proposed delay guaranteed HCCA scheduling scheme is compared with that of original HCCA scheme specified in 802.11p standard and other 2 HCCA improved schemes by the simulation experiments. The simulation results demonstrate that the proposed solution could highly fulfill the transmission delay requirements with a better channel utility and less loss rates than those by the standard HCCA scheme and other 2 schemes.

Novel Communication Protocol for the EV Charging/Discharging Service Based on VANETs

In this paper, we take advantage of the communication systems which will be adopted for the new vehicle generations in near future and we propose a new electric vehicle (EV) charge/discharge service scheme for large EV density through vehicular ad-hoc networks communications. First, we present a communication protocol for the EV charging/discharging protocol with the uplink and the downlink EV charge /discharge frame format exchanged between EVs and smart grid. Second, we propose our channel access scheme based on a distributed time slot assignment model (DTSA) to allow the EV charging/discharging service negotiations with smart grid before plug-in phase. This DTSA scheme, which is a contention-free channel access mechanism, can improve the EV charging/discharging service access by increasing the successful rate of channel reservation both on control channel (CCH) and service channel (SCH). We propose also three algorithms to manage the EV charge/discharge service reservation and negotiation, respectively, on CCH and SCH. Finally, extensive simulations with NS-2 and MATLAB are conducted to validate the proposed approach and demonstrate the efficiency and effectiveness of the proposed compared to IEEE802.11p and VeMAC while satisfying the defined constraints.

A Novel IEEE 802.15.4e DSME MAC for Wireless Sensor Networks.

IEEE 802.15.4e standard proposes Deterministic and Synchronous Multichannel Extension (DSME) mode for wireless sensor networks (WSNs) to support industrial, commercial and health care applications. In this paper, a new channel access scheme and beacon scheduling schemes are designed for the IEEE 802.15.4e enabled WSNs in star topology to reduce the network discovery time and energy consumption. In addition, a new dynamic guaranteed retransmission slot allocation scheme is designed for devices with the failure Guaranteed Time Slot (GTS) transmission to reduce the retransmission delay. To evaluate our schemes, analytical models are designed to analyze the performance of WSNs in terms of reliability, delay, throughput and energy consumption. Our schemes are validated with simulation and analytical results and are observed that simulation results well match with the analytical one. The evaluated results of our designed schemes can improve the reliability, throughput, delay, and energy consumptions significantly.

Packet-Size Optimization for Multiple-Input Multiple-Output Cognitive Radio Sensor Networks-Aided Internet of Things

The determination of optimal packet size (OPS) for a cognitive radio-assisted sensor networks (CRSNs) architecture is non-trivial. State of the art in this area describes various complex techniques to determine OPS for CRSNs. However, it is observed that under high interference from the surrounding users, it is not possible to determine a feasible OPS of data transmission under the simple point-to-point CRSN topology. This is contributed primarily to the peak transmit power constraint of the cognitive nodes. To address this specific challenge, this paper proposes a multiple-input multiple output-based CRSNs (MIMO-CRSNs) architecture for futuristic technologies, such as Internet of Things and machine-to-machine communications. A joint optimization problem is formulated, considering network constraints, such as the overall end-to-end latency, interference duration caused to the non-cognitive users, average BER, and transmit power. We propose our Algorithm 1 based on the generic exhaustive search technique to solve the optimization problem. Furthermore, a low complexity suboptimal Algorithm 2 based on solving classical Karush–Kuhn–Tucker conditions is proposed. These algorithms for MIMO-CRSNs are implemented in conjunction with two different channel access schemes. These channel access schemes are time-slotted distributed cognitive medium access control denoted as MIMO-DTS-CMAC and CSMA/CA-assisted centralized common control channel-based cognitive medium access control denoted as MIMO-CC-CMAC. Simulations reveal that the proposed MIMO-CRSN outperforms the conventional point-to-point CRSN in terms of overall energy consumption. Moreover, the proposed Algorithm 1 and Algorithm 2 show a perfect match, and the implementation complexity of Algorithm 2 is less than Algorithm 1 . Algorithm 1 takes almost 680 ms to execute and provides OPS value for a given number of users, whereas Algorithm 2 takes 4–5 ms on average to find the OPS for the proposed MIMO-CRSN framework.

Proportional Fairness-Based Resource Allocation for LTE-U Coexisting With Wi-Fi

To further boost the performance of LTE to meet the ever-increasing mobile traffic demand in a cost-effective way, applying LTE in unlicensed spectrum, known as LTE-U technology, is considered as a promising complementary solution for achieving the ultra-capacity foreseen in 5G and beyond. In the unlicensed spectrum, LTE-U will share the channel with other unlicensed networks, e.g., Wi-Fi. However, the centralized control architecture of LTE networks is inherently different from the distributed channel access of Wi-Fi network, which poses great challenges to achieve fair coexistence of the two networks. To this end, in this paper, we propose a cross-layer proportional fairness (PF)-based framework to jointly optimize the protocol parameters of the medium access control layer and physical layer of an LTE-U network. Specifically, to achieve throughput-oriented PF between the two heterogeneous networks, the cross-layer optimization framework can be decoupled into a device number weighted time occupation ratio-oriented PF optimization problem and a channel-power allocation-based instantaneous transmission rate-oriented PF optimization problem. Given that LTE-U base stations adopt a listen-before-talk-based channel access scheme, the interactions between the LTE-U and the Wi-Fi networks are modeled by two interactive Markov chains. The effectiveness and the superior performance of the proposed cross-layer PF-based optimization framework are demonstrated and verified by simulations.

An Efficient Channel Access Scheme for Vehicular Ad Hoc Networks

Vehicular Ad Hoc Networks (VANETs) are getting more popularity due to the potential Intelligent Transport Systems (ITS) technology. It provides many efficient network services such as safety warnings (collision warning), entertainment (video and voice), maps based guidance, and emergency information. VANETs most commonly use Road Side Units (RSUs) and Vehicle-to-Vehicle (V2V) referred to as Vehicle-to-Infrastructure (V2I) mode for data accessing. IEEE 802.11p standard which was originally designed for Wireless Local Area Networks (WLANs) is modified to address such type of communication. However, IEEE 802.11p uses Distributed Coordination Function (DCF) for communication between wireless nodes. Therefore, it does not perform well for high mobility networks such as VANETs. Moreover, in RSU mode timely provision of data/services under high density of vehicles is challenging. In this paper, we propose a RSU-based efficient channel access scheme for VANETs under high traffic and mobility. In the proposed scheme, the contention window is dynamically varied according to the times (deadlines) the vehicles are going to leave the RSU range. The vehicles with shorter time deadlines are served first and vice versa. Simulation is performed by using the Network Simulator (NS-3) v. 3.6. The simulation results show that the proposed scheme performs better in terms of throughput, backoff rate, RSU response time, and fairness.

PC-MAC: A Prescheduling and Collision-Avoided MAC Protocol for Underwater Acoustic Sensor Networks

The impact of the acoustic modem with long preamble characteristic on the collision feature of the media access control scheme in underwater acoustic sensor networks (UANs) is evaluated. It is observed that the collision probability is relatively high due to the extremely long duration of preamble. As a result, UANs generally have much lower network throughput. To address this problem, a prescheduling MAC protocol named PC-MAC for UANs is proposed, which leverages a novel prescheduling scheme for the exchange of control packet to alleviate the collision probability among control packets. PC-MAC is a reservation-based channel access scheme. In the proposed protocol, an extra guard time is introduced to avoid the influence of dynamic spatial-temporal uncertainty of the sender and receiver positions. Simulation results show that PC-MAC outperforms classic reservation-based MAC protocol named SFAMA in terms of network goodput and end-to-end delay and lowers collision probability among control packets in two representative network scenarios.

Proportional bandwidth allocation with consideration of delay constraint over IEEE 802.11e-based wireless mesh networks

Wireless mesh networks (WMNs) extend the limited transmission coverage of wireless LANs by enabling users to connect to the Internet via a multi-hop relay service provided by wireless mesh routers. In such networks the quality of experience (QoE) depends on both the user location relative to the Internet gateway and the traffic load. Various channel access or queue management schemes have been proposed for achieving throughput fairness among WMN users. However, delay and bandwidth utilization efficiency of such schemes may be unacceptable for real-time applications. Accordingly, the present study proposes a proportional bandwidth allocation scheme with a delay constraint consideration for enhancing the QoE of users of WMNs based on the IEEE 802.11e standard. An analytical model of the proposed scheme is provided. Moreover, the performance of the proposed scheme is systematically compared with that of existing bandwidth allocation methods. The simulation results show that the proposed scheme outperforms previously proposed schemes in terms of both an improved throughput fairness among the WMN users and a smaller end-to-end transmission delay.

A Low Collision and High Throughput Data Collection Mechanism for Large-Scale Super Dense Wireless Sensor Networks.

Super dense wireless sensor networks (WSNs) have become popular with the development of Internet of Things (IoT), Machine-to-Machine (M2M) communications and Vehicular-to-Vehicular (V2V) networks. While highly-dense wireless networks provide efficient and sustainable solutions to collect precise environmental information, a new channel access scheme is needed to solve the channel collision problem caused by the large number of competing nodes accessing the channel simultaneously. In this paper, we propose a space-time random access method based on a directional data transmission strategy, by which collisions in the wireless channel are significantly decreased and channel utility efficiency is greatly enhanced. Simulation results show that our proposed method can decrease the packet loss rate to less than in large scale WSNs and in comparison with other channel access schemes for WSNs, the average network throughput can be doubled.

CoR-MAC: Contention over Reservation MAC Protocol for Time-Critical Services in Wireless Body Area Sensor Networks.

Reserving time slots for urgent data, such as life-critical information, seems to be very attractive to guarantee their deadline requirements in wireless body area sensor networks (WBASNs). On the other hand, this reservation imposes a negative impact on performance for the utilization of a channel. This paper proposes a new channel access scheme referred to as the contention over reservation MAC (CoR-MAC) protocol for time-critical services in wireless body area sensor networks. CoR-MAC uses the dual reservation; if the reserved time slots are known to be vacant, other nodes can access the time slots by contention-based reservation to maximize the utilization of a channel and decrease the delay of the data. To measure the effectiveness of the proposed scheme against IEEE 802.15.4 and IEEE 802.15.6, we evaluated their performances with various performance indexes. The CoR-MAC showed 50% to 850% performance improvement in terms of the delay of urgent and time-critical data according to the number of nodes.

Toward Optimal Adaptive Wireless Communications in Unknown Environments

Designing efficient channel access schemes for wireless communications without any prior knowledge about the nature of environments has been a very challenging issue, especially when the channel states distribution of all spectrum resources could be entirely or partially stochastic and/or adversarial at different time and locations. In this paper, we propose an adaptive channel access algorithm for wireless communications in unknown environments based on the theory of multi-armed bandits (MAB) problems. By automatically tuning two control parameters, i.e., learning rate and exploration probability, our algorithms are capable of finding the optimal channel access strategies and achieving the almost optimal learning performance over time under our defined four typical regimes for general unknown environments, e.g., the stochastic regime where channels follow some unknown i.i.d process, the adversarial regime where all channels are suffered by adversarial jamming attack, the mixed stochastic and adversarial regime where a subset of channels are attacked and the contaminated stochastic regime where occasionally adversarial events contaminate the stochastic channel process, etc. To reduce the implementation time and space complexity, we further develop an enhanced algorithm by exploiting the internal structure of the selection of channel access strategy. We conduct extensive simulations in all these regimes to validate our theoretical analysis. The quantitative performance studies indicate the superior throughput gain and the flexibility of our algorithm in practice, which is resilient to both oblivious and adaptive jamming attacks with different intelligence and any attacking strength that ranges from no-attack to the full-attack of all spectrum resources.

Aging Aware Random Channel Access for Battery-Powered Wireless Networks

Energy harvesting is becoming a key technology in mobile wireless networks, and especially sensor systems. The bursty nature of energy arrival generated by renewable resources may apply considerable stress to the battery, and degrade its state of health (SoH) by generating deep charging and discharging cycles. In this letter, a novel random channel access scheme is proposed that tunes transmission parameters to reduce SoH degradation while preserving the network performance.

Distributed Optimization of Channel Access Strategies in Reactive Cognitive Networks

In reactive cognitive networks, the channel access and the transmission decisions of the cognitive terminals have a long-term effect on the network dynamics. When multiple cognitive terminals coexist, the optimization and implementation of their strategy is challenging and may require considerable coordination overhead. In this paper, such challenge is addressed by a novel framework for the distributed optimization of transmission and channel access strategies. The objective of the cognitive terminals is to find the optimal action distribution depending on the current network state. To reduce the coordination overhead, in the proposed framework the cognitive terminals distributively coordinate the policy, whereas the action in each individual time slot is independently selected by the terminals. The optimization of the transmission and channel access strategy is performed iteratively by using the alternate convex optimization technique, where at each iteration a cognitive terminal is selected to optimize its own action distribution while assuming fixed those of the other cognitive terminals. For a traditional primary–secondary user network configuration, numerical results show that the proposed algorithm converges to a stable solution in a small number of iterations, and a limited performance loss with respect to the perfect coordinated case.

V2V QoS Guaranteed Channel Access in IEEE 802.11p VANETs

IEEE 802.11p Wireless Access in the Vehicular Environment (WAVE) has been serving as the de facto wireless protocol for a Vehicular Ad hoc Network (VANET) with the explosive growth of vehicular applications. These applications require guaranteed Quality-of-Service (QoS). However, the fundamental channel access mechanism of WAVE, Enhanced Distributed Channel Access (EDCA), is not able to provide guaranteed QoS due to the unpredictable random access. To remedy this problem, we propose a novel channel access scheme, called Earliest Deadline First based Carrier Sense Multiple Access (EDF-CSMA). EDF-CSMA based on EDCA dynamically adjusts the priority of real-time streaming to avoid collision and introduces an admission control policy according to time constraints to provide guaranteed QoS in multi-channel environments. An analytical model is carried out to study and compare the channel utilization of EDF-CSMA and QoS-aware Hybrid Coordination Function (HCF) controlled channel access (HCCA) method. The result shows that 60 percent of channel utilization is improved by EDF-CSMA. Additionally, real video-based simulations are conducted to evaluate the performance of EDF-CSMA and the existing EDCA method. The results show that EDF-CSMA reaches better QoS support than EDCA while maintaining efficient channel utilization.