Channel Access Mechanism Research Articles

On medium access control schemes for wireless networks in the millimeter-wave and Terahertz bands

Millimeter wave (mmW) and Terahertz band (THz) play important roles for future wireless communications to support ultra-high data rates. However, the high propagation loss and inherent directivity features pose critical challenges on the medium access control (MAC) protocol design to fully exploit their potential benefits, including deafness, control channel selection mechanism, line-of-sight (LoS) blockage, mobility management and spatial reuse strategy. To address these challenges, in-depth literature survey is conducted on MAC protocols for the mmW and THz bands wireless networks in this paper. A taxonomy of the MAC protocols based on their network architectures and the channel access mechanisms is presented. Furthermore, emphasizing the benefits and requirements of the MAC design choices, extensive qualitative comparison is described on the advantages and disadvantages among the different directional MAC design choices. Numerical evaluations on delay, network throughput, outage probability, and fairness are detailed to guide the corresponding performance-oriented design selections. Finally, some open problems and possible future directions on the mmW and THz MAC design are respectively elaborated.

Performance Analysis of License Assisted Access LTE with Asymmetric Hidden Terminals

License Assisted Access (LAA) LTE (LTE-LAA) is a new type of LTE that aggregates the licensed LTE bands with the unlicensed bands via carrier aggregation. To operate in unlicensed bands, LTE-LAA adopts the listen-before-talk policy and designs its channel access mechanism similar to WLAN's DCF. In this paper, we consider an LAA network consisting of an LTE-LAA eNB coexisting with a Wi-Fi STA, and capture the {\em asymmetric hidden terminal problem} where the eNB recognizes the STA while the opposite is not true, which is caused by the asymmetric CCA thresholds between them. We model the network as a joint Markov chain (MC) consisting of two individual MCs, and derive its steady-state probabilities, throughput, and channel access delay along with other key metrics like transmit, busy, collision, and doubling probabilities. Through extensive evaluation, we confirm that the proposed model well predicts the dynamics of the LAA network, and identify important design guidelines for fair coexistence between LTE-LAA and WLAN as follows. First, LTE-LAA should design its contention window (CW) doubling policy by considering Wi-Fi's packet duration and subframe-dependent collision probabilities. Second, there exists a tradeoff between throughput and channel access delay, according to which the CW doubling policy should be adapted.

Toward Massive Machine Type Communications in Ultra-Dense Cellular IoT Networks: Current Issues and Machine Learning-Assisted Solutions

The ever-increasing number of resource-constrained Machine-Type Communication (MTC) devices is leading to the critical challenge of fulfilling diverse communication requirements in dynamic and ultra-dense wireless environments. Among different application scenarios that the upcoming 5G and beyond cellular networks are expected to support, such as eMBB, mMTC and URLLC, mMTC brings the unique technical challenge of supporting a huge number of MTC devices, which is the main focus of this paper. The related challenges include QoS provisioning, handling highly dynamic and sporadic MTC traffic, huge signalling overhead and Radio Access Network (RAN) congestion. In this regard, this paper aims to identify and analyze the involved technical issues, to review recent advances, to highlight potential solutions and to propose new research directions. First, starting with an overview of mMTC features and QoS provisioning issues, we present the key enablers for mMTC in cellular networks. Along with the highlights on the inefficiency of the legacy Random Access (RA) procedure in the mMTC scenario, we then present the key features and channel access mechanisms in the emerging cellular IoT standards, namely, LTE-M and NB-IoT. Subsequently, we present a framework for the performance analysis of transmission scheduling with the QoS support along with the issues involved in short data packet transmission. Next, we provide a detailed overview of the existing and emerging solutions towards addressing RAN congestion problem, and then identify potential advantages, challenges and use cases for the applications of emerging Machine Learning (ML) techniques in ultra-dense cellular networks. Out of several ML techniques, we focus on the application of low-complexity Q-learning approach in the mMTC scenarios. Finally, we discuss some open research challenges and promising future research directions.

Performance Analysis on IEEE 802.11ah Standard with Enhanced Distributed Channel Access Mechanism

IEEE 802.11ah is a new task group on the IEEE 802.11 standard designed to work on the 900 MHz. It is with a range of communication coverage up to 1kilometer, lower energy consumption, and up to 8191 stations. There are two types of STAs in 802.11ah: sensor type to support sensor service and non-sensor type for offload service. In this research, it only focuses on non-sensor STA. For non-sensor STA, maximizing throughput is more important than power consumption. This research aims to see the performance of IEEE 802.1 1ah with Enhanced Distributed Channel Access (EDCA). To achieve that purpose, a mechanism is needed to provide guarantees various services required by theSTA. EDCA is an access mechanism used to set the Quality of Service (QoS) for the IEEE 802.11 standard through modifications in MAC layer. In this research,it focuses on one of the EDCA parameters, Arbitration Inter-Frame Space (AIFS). In addition, this research also focuses on the 802.11ah feature is Restricted Access Window (RAW) by changing the number of the RAW groups. From the results of the research, it is found that the improvement scheme with Arbitration Inter-Frame Space Number (AIFSN) value AC BK = 2, AC BE = 1, AC VI = 1, AC VO = 1 has better performance compared to the default scheme with AIFSN value AC BK = 7, AC BE = 3, AC VI = 2, AC VO = 2) with an average throughput of 1.504598 Mbps, average overall delay of 0.066242 second and average PDR of 62%. In addition, changes in the number of RAW groups and RAW slots affect network performance. This feature can improve the value of throughput, average delay, and Packet Delivery Ratio. The goals of this research is to know the effect of AIFSN value changes on AIFSN parameters, variation of RAW group and RAW slot number to throughput,average delay and packet delivery ratio.

TH-PPM with non-coherent detection for multiple access in electromagnetic wireless nanocommunications

Terahertz band (0.1–10 THz)-based electromagnetic nanocommunications could advance several nanotechnology applications in the biomedical, environmental, and military fields. One of the fundamental challenges with nanocommunications is the need for an appropriate modulation and channel access mechanism. In multi-user nanocommunications, detrimental effects of path loss and interference could pose a significant problem for multiple nano-devices trying to access the channel concurrently. This would result in retransmissions, which is barely affordable at the nano-level due to the minute size and energy constraints of nano-devices. In this paper, time-hopping (TH) combined with M-ary pulse position modulation (PPM) is proposed as a modulation and multiple access scheme for multi-user nanocommunications systems. PPM, being the most energy-efficient modulation scheme, with TH would allow nano-devices to communicate simultaneously with greater efficiency. Decoding at the receiver is done after non-coherent detection. The symbol-error rate (SER) in the presence of multi-user interference is evaluated in terms of signal-energy-to-noise ratio and the number of interfering users. Moreover, capacity of the system is also evaluated in terms of bits per symbol for different design parameters. Numerical results show that the SER and capacity of the system can be improved by choosing appropriate TH-PPM parameters for a given network condition. The comparisons of simulation results for TH-PPM with another existing scheme witnesses an improved energy efficiency and reduced computational complexity.

An IEEE 802.11ah-based scalable network architecture for Internet of Things

IEEE 802.11ah is proven to be a suitable communication standard for Internet of Things. It supports a wide range of modulation and coding schemes (MCSs) along with different data rates. The Restricted Access Windows (RAW)-based channel access mechanism facilitates scalable communication among a large number of devices. However, due to the absence of RAW size adjustment, it fails to optimally utilize the resources in a dynamic network environment. In this paper, we propose a method to estimate the RAW size based on traffic loads and provide relay node support for stations to use different MCSs. The relay nodes dynamically allocate bandwidth to stations belonging to different relay groups. The proposed scheme is seamlessly assimilated into 802.11ah which shows significant performance improvement in terms of throughput and delay.

A Timer-Based Distributed Channel Access Mechanism in Networked Control Systems

We consider a system consisting of multiple heterogeneous control subsystems sharing a common communication resource for accomplishing their control tasks. Despite the numerous advantages that such networked control systems (NCSs) offer, their implementation is limited in practice due to the limited communication resources. We propose a novel distributed approach for the resource allocation problem in NCSs by which the subsystems can coordinate to access the network. More specifically, we develop a deterministic distributed scheme with which the subsystem with the highest cost is selected, based only on local information without requiring explicit communication between the subsystems. The efficiency of our scheme is demonstrated via simulations and it is compared with a centralized approach and other relevant approaches.

Cross-layer design benchmark for throughput maximization with fairness and delay constraints in DCF systems

This paper proposes a cross-layer design for the stations (STAs) in a distributed coordination function (DCF) network. By selecting the modulation scheme, coding scheme, and packet length of each STA in the network, the design aims to maximize the total throughput of all the STAs and satisfy the minimum throughput requirement or delay requirement of each STA, thus addressing the fairness and delay issues. The proposed scheme applies to the system where each STA employs a contention based channel access mechanism, Furthermore, unlike the existing optimization schemes, it takes two important factors, changeable data rate and changeable packet error rate (PER), into consideration. Using an existing Markov chain model to predict the performance of the STAs, we propose an approach that updates the selection of each STA sequentially, thus avoiding the large complexity from the exhaustive search. Many issues are discussed based on the numerical results, including how the approximations in our design affect the processing time and result of the design, how the change of one STA affects the performance of the other STAs, how the minimum throughput constraints affect the fairness and total throughput, how to select these constraints to satisfy the delay requirements, etc.

Coexistence of DC and CSMA in SRD channel access and resilience to LTE interference: A simulator‐based analysis

AbstractThe foreseen increased use of short‐range devices (SRDs) will boost the competition for radio channel access in license‐exempt frequency bands. Therefore, it is important to find out the most efficient SRD configurations in terms of their performance in high‐contention scenarios; moreover, it is crucial to ensure that SRD networks do not impair the radio systems that operate in neighboring licensed spectrum, and vice versa. This paper addresses the previous issues by simulating a building automation application scenario, where 2 channel access mechanisms, namely duty cycling (DC) and carrier sense multiple access (CSMA), are evaluated independently and in coexisting scenarios, and, also, in the presence of a Long‐Term Evolution (LTE) user equipment. The CSMA protocol analysis shows that very high or very low transmission powers decrease its performance, and thus, either this parameter has to be calibrated or the gateways location has to be adjusted; for the DC protocol, its performance is only affected by the number of gateways within the SRD network, which should be as high as possible. Regarding the coexistence of the DC and CSMA schemes, the results show that CSMA‐based SRDs can successfully operate in the presence of a significant number of DC‐based SRDs, whereas the contrary is not true. Lastly, it is proven that an LTE user equipment may harm the SRD network, although this effect can be mitigated by adjusting the SRDs transmission power; furthermore, the SRDs interference on LTE systems is found to be negligible.

On Large Capacity and Energy Efficiency Indoor Location System Based on WSN

The indoor information of location has been used widely and it’s of great significance in our society and daily life. Most indoor positioning methods are based on Bluetooth, RFID, ZigBee and other technologies. In some scenarios, especially in the harsh industrial manufacturing environment, these technologies mainly based on CSMA are often inadequate to meet the needs in large capacity, low power consumption and anti-interference. We propose an indoor location system based on wireless sensor network to reduce the limitation. It adopts TDMA as channel access mechanism to ensure the efficiency and instantaneity of the indoor location system. A reference node working in both 2.4GHz and 780MHz is designed to combine penetrability and energy conservation. We improve the positioning algorithm based on RSSI by using the K-means algorithm. The experiment shows that the indoor positioning system basically satisfies the demand in reliability and positioning accuracy.

Intelligent slots allocation for dynamic differentiation in IEEE 802.15.6 CSMA/CA

eHealth applications have become essential in everyday life healthcare especially for elderly and sick individuals. To provide efficiency to such applications, many standards emerged for WBANs. However, WBANs standards showed their limits in terms of QoS and priorities differentiation depending on applications need. In this paper, we investigate IEEE 802.15.6 MAC performance efficiency and we define TA-802.15.6, an enhanced IEEE 802.15.6 CSMA/CA channel access mechanism. We aim to differentiate all IEEE 802.15.6 priorities traffics and to improve IEEE 802.15.6 based networks performances. Our main contribution is the enhancement of IEEE 802.15.6 CSMA/CA retransmission and packet drop processes. We also defined a new algorithm for dynamic backoff bounds assignment according to IEEE 802.15.6 priorities and to the network traffic state. We make an analytical evaluation through a new 4D Markov chain and by simulation based on Castalia. Results validate that the enhanced IEEE 802.15.6 CSMA/CA version provides a better service differentiation through accentuating priority differentiation and a better QoS in terms of reliability, throughput and energy consumption.

Transmission Capacity Analysis for Vehicular Ad Hoc Networks

Traditional studies focused on the transmission capacity of vehicular ad hoc network (VANET) contains two deficiencies: the lack of a realistic model mimicking the behaviors of vehicles and the failure to consider the impacts from enhanced distributed channel access (EDCA) mechanisms applied by IEEE 802.11p. In this paper, the car-following model is introduced to describe the distribution of vehicles, and an EDCA-based linear VANET model is analyzed. Compared to previous works, a tighter transmission capacity upper bound in a large-scale fading environment is calculated. Furthermore, under Rayleigh fading channels, an elementary expression of transmission capacity fitting a sparse vehicles scenario and an upper bound of transmission capacity applicable to a dense scenario are obtained. In conclusion, the transmission capacity of a linear VANET is illustrated by the elementary expression in a sparse vehicles scenario and the upper bound in a dense vehicles scenario. The simulation results are well constrained by the proposed theoretical expression and upper bound.

Delay and Reliability of Load-Based Listen-Before-Talk in LAA

With the release of the 5 GHz unlicensed spectrum has emerged licensed-assisted access, in which long-term evolution (LTE) operators compete with Wi-Fi users for a share of the unlicensed spectrum so as to augment their licensed spectrum. Subsequently, there has been the need to develop a LTE channel access mechanism that enables harmonious coexistence between Wi-Fi and LTE. Load-based listen-before-talk (LB-LBT) has been adopted as this LTE channel access mechanism by the 3rd Generation Partnership Project (3GPP). Theoretical modelling of LB-LBT schemes has focused on throughput and fair channel-time sharing between Wi-Fi and LTE technologies. We explore a LB-LBT scheme that belongs to LBT category 4, as recommended by the 3GPP, and develop a model for the distribution of the medium access control (MAC) delays experienced by the Wi-Fi packets and LTE frames. The model, validated by simulations, reveals design insights that can be used to dynamically adjust the LB-LBT parameters not only to achieve channel-time fairness, but also to guarantee MAC-delay bounds, with specified probability.

Revisiting of Channel Access Mechanisms in Mobile Wireless Networks through Exploiting Physical Layer Technologies

The wireless local area networks (WLANs) have been widely deployed with the rapid development of mobile devices and have further been brought into new applications with infrastructure mobility due to the growth of unmanned aerial vehicles (UAVs). However, the WLANs still face persistent challenge on increasing the network throughput to meet the customer’s requirement and fight against the node mobility. Interference is a well‐known issue that would degrade the network performance due to the broadcast characteristics of the wireless signals. Moreover, with infrastructure mobility, the interference becomes the key obstacle in pursuing the channel capacity. Legacy interference management mechanism through the channel access control in the MAC layer design of the 802.11 standard has some well‐known drawbacks, such as exposed and hidden terminal problems, inefficient rate adaptation, and retransmission schemes, making the efficient interference management an everlasting research topic over the years. Recently, interference management through exploiting physical layer mechanisms has attracted much research interest and has been proven to be a promising way to improve the network throughput, especially under the infrastructure mobility scenarios which provides more indicators for node dynamics. In this paper, we introduce a series of representative physical layer techniques and analyze how they are exploited for interference management to improve the network performance. We also provide some discussions about the research challenges and give potential future research topics in this area.

Performance Analysis of IEEE 802.11p Safety Message Broadcast With and Without Relaying at Road Intersection

Dedicated short-range communication (DSRC), which is an essential part of vehicle-to-vehicle/infrastructure communication to enhance the road safety, is often characterized by the IEEE 802.11p standard. Numerous works have been done on the DSRC safety message broadcasting performance for highway scenario. However, up to date, no work has been done on the performance of the IEEE 802.11p safety message broadcasting for the road-intersection scenario in urban environment. An intersection scenario is different from a highway scenario. In a highway scenario, it is often been considered that all the vehicles have the same communication range as well as the same carrier sensing range. However, this is not the case for the intersection scenario, where there exist a lot of obstructions, such as buildings and urban canyons. In an intersection, the communication and carrier sensing ranges of a vehicle heavily depend on the location of that vehicle. This paper first analyzes and then provides solution on improving the broadcasting performance of the DSRC safety message at an intersection while considering the IEEE 802.11p enhanced distributed channel access mechanism. To facilitate different communication and carrier sensing ranges of different vehicles, we divide the intersection region into few parts/areas based on an empirically validated path loss model. We present an analytical study on the packet reception rates and channel access delay which is applicable for the different positions of transmitters and receivers in the intersection areas. The analytical results are verified by the NS-3 simulation. From the results, we find that the overall delivery ratio is very poor when the broadcasting vehicle is not close enough to the intersection-center. To improve the overall broadcast performance of such scenarios, we employ a road side unit (RSU) at the intersection-center to relay the safety messages once. We show the performance improvement via relaying while first using omni-directional and then using special sector antennas, the so-called bidirectional antenna, at the RSU. From the results, it is shown that relaying with the omni-directional antenna gives moderate improvement on the overall delivery ratio, while a significant improvement can be achieved by relaying with sector antenna.

A Delay and Energy Efficient Poll-Based MAC Protocol for Wireless Body Area Networks

A number of tiny sensor nodes are strategically placed in and around the human body to obtain physiological information. The sensor nodes are connected to a coordinator or a data collector to form a wireless body area network (WBAN). WBAN consists of variety of medical and non-medical applications with aggregate data rate requirement ranging from few bytes per second to 10 Mbps. These applications are having relatively different energy saving, reliability and quality of service (QoS) requirements. For example, emergency medical data are highly erratic but should be transferred with high reliability and minimum delay, whereas electrocardiogram and electroencephalogram applications are constant bit rate traffic which need to be transferred with moderate reliability. Additionally, non-medical applications include variable bit rate traffic and their jitter and delay requirements must also be met. On the above, a sensor node should spend minimum energy and conserve power to increase its life time in the network. The existing media access control (MAC) protocols present in various short and medium range wireless technologies such as 802.11 and 802.15.4 have been designed for specific purposes, and therefore, do not fulfill the diverse performance requirements across all WBAN applications. In this paper, we propose a poll-based MAC protocol, PMAC for WBAN, which can meet such diversified functional requirements of various WBAN applications. In particular, we introduce few concepts in polling based channel access mechanism to make an energy efficient and QoS aware MAC protocol. The design has been validated by obtaining the performance of proposed PMAC protocol through simulation.

Performance Analysis of the IEEE 802.11p Multichannel MAC Protocol in Vehicular Ad Hoc Networks.

Vehicular Ad Hoc Networks (VANETs) employ multichannel to provide a variety of safety and non-safety applications, based on the IEEE 802.11p and IEEE 1609.4 protocols. The safety applications require timely and reliable transmissions, while the non-safety applications require efficient and high throughput. In the IEEE 1609.4 protocol, operating interval is divided into alternating Control Channel (CCH) interval and Service Channel (SCH) interval with an identical length. During the CCH interval, nodes transmit safety-related messages and control messages, and Enhanced Distributed Channel Access (EDCA) mechanism is employed to allow four Access Categories (ACs) within a station with different priorities according to their criticality for the vehicle’s safety. During the SCH interval, the non-safety massages are transmitted. An analytical model is proposed in this paper to evaluate performance, reliability and efficiency of the IEEE 802.11p and IEEE 1609.4 protocols. The proposed model improves the existing work by taking serval aspects and the character of multichannel switching into design consideration. Extensive performance evaluations based on analysis and simulation help to validate the accuracy of the proposed model and analyze the capabilities and limitations of the IEEE 802.11p and IEEE 1609.4 protocols, and enhancement suggestions are given.

Fairness vs. Performance in Rel-13 LTE Licensed Assisted Access

Wireless spectrum being a valuable resource, a large number of both non-profit and for-profit users rely on its unlicensed parts, usually to provide some sort of local area wireless coverage. When the cellular vendors and service providers expressed interest in the unlicensed spectrum, the incumbent community started to fear that the new technology would not respect the existing users. And although members of the incumbent community strongly influenced the design of licensed assisted access (LAA) in 3GPP, the fear has not dispersed yet. Representing a vendor with stakes in both communities, we attempt to disperse the fear by providing insight on the question of fairness and performance of LAA, openly discussing why it should generate less interference than WiFi and why it could be otherwise. We augment the discussion with insightful simulations, looking how detailed parameters of the channel access mechanism influence LAA's fairness and performance. Our investigations show that in common scenarios LAA is a fair neighbor to WiFi as is, and even in an extreme scenario only small adjustments to the channel access mechanism are needed to achieve the same outcome.

End-to-End Backlog and Delay Bound Analysis for Multi-Hop Vehicular Ad Hoc Networks

Vehicular ad hoc network (VANET) is able to facilitate data exchange among vehicles and provides diverse data services. Intuitively, end-to-end backlog and delay bounds are considered significant metrics to evaluate the quality of service in VANETs. In order to analyze how the multi-hop transmission impacts the delay performance, we model the multi-hop service process into a virtualized single service in a min-plus convolution form. To obtain multi-hop end-to-end backlog and delay bound, we consider the stochastic network traffic characteristics and the highly dynamic channel environment under the static priority, first in first out, and earliest deadline first scheduling policies by applying the martingale theory. The IEEE 802.11p enhanced distributed channel access mechanism is also adopted to analyze the access performance in the MAC sub-layer. With three kinds of real wireless data traces, i.e., VoIP, gaming, and UDP, we verify our algorithm by considering the double Nakagami- $m$ fading channel model among vehicles. From the simulation results, we can see that the supermartingale end-to-end backlog and delay bound are remarkably tight to the real simulation results when compared with the existing standard bounds. The effect of the number of vehicles on the highway on the end-to-end backlog and delay performance is also investigated.

Design and Analysis of a Low Latency Deterministic Network MAC for Wireless Sensor Networks.

The IEEE 802.15.4e standard has four different superframe structures for different applications. Use of a low latency deterministic network (LLDN) superframe for the wireless sensor network is one of them, which can operate in a star topology. In this paper, a new channel access mechanism for IEEE 802.15.4e-based LLDN shared slots is proposed, and analytical models are designed based on this channel access mechanism. A prediction model is designed to estimate the possible number of retransmission slots based on the number of failed transmissions. Performance analysis in terms of data transmission reliability, delay, throughput and energy consumption are provided based on our proposed designs. Our designs are validated for simulation and analytical results, and it is observed that the simulation results well match with the analytical ones. Besides, our designs are compared with the IEEE 802.15.4 MAC mechanism, and it is shown that ours outperforms in terms of throughput, energy consumption, delay and reliability.