Medium Access Control Design Research Articles

Random Access Protocol With Channel Oracle Enabled by a Reconfigurable Intelligent Surface

The widespread adoption of Reconfigurable Intelligent Surfaces (RISs) in future practical wireless systems is critically dependent on the integration of the RIS into higher-layer protocols beyond the physical (PHY) one, an issue that has received minimal attention in the research literature. In light of this, we consider a classical random access (RA) problem, where uncoordinated users’ equipment (UEs) transmit sporadically to an access point (AP). Differently from previous works, we ponder how a RIS can be integrated into the design of new medium access control (MAC) layer protocols to solve such a problem. We consider that the AP is able to control a RIS to change how its reflective elements are configured, namely, the RIS configurations. Thus, the RIS can be opportunistically controlled to favor the transmission of some of the UEs without the need to explicitly perform channel estimation (CHEST). We embrace this observation and propose a RIS-assisted RA protocol comprised of two modules: Channel Oracle and Access. During channel oracle, the UEs learn how the RIS configurations affect their channel conditions. During the access, the UEs tailor their access policies using the channel oracle knowledge. Our proposed RIS-assisted protocol is able to increase the expected throughput by approximately 60% in comparison to the slotted ALOHA (S-ALOHA) protocol.

Exclusive-Region-Map-Based Medium Access Control in Mobile Networks With Directional Antennas Through Deep Interference Learning

The medium access control (MAC) design in mobile networks with directional antennas is challenging due to the difficulty of defining the exact RF interference range between two neighboring directional links and the frequent changes of interference range due to node mobility. This research targets directional data reception (Rx) and transmission (Tx) coordination issues based on the computation of directional interference ranges from nearby directional links. An innovative MAC mechanism is designed with three features: (1) ER-map, i.e., the spatial expression of exclusive region (ER) model in the format of a heatmap. The ER-map helps to determine the directional interference range in typical communication scenarios. Different ER-map cases are analyzed based on the spatial layout differences for two nearby directional links. (2) Spatio-temporal ER-map evolution prediction: a Spatio-Temporal Residual Network (ST-ResNet+) model is used to describe the spatial correlations (for the ERs among neighboring links) and temporal correlations (for the ERs across different time instants) as well as the ER map evolution patterns. Such a Deep ST-ResNet+ model is used to predict the next-time ER map’s snapshot. (3) Optimized directional MAC protocol based on ER map predictions: The ST-ResNet+ prediction results are used to determine the MAC operations, such as Tx/Rx schedule arrangement in the one-hop area, sending rate adjustments, etc. Comprehensive simulations are conducted to validate the throughput efficiency for the proposed directional MAC scheme.

Intelligent Terahertz Medium Access Control (MAC) for Highly Dynamic Airborne Networks

The Terahertz (THz) link provides over 100 Gbps of data transmission rate. However, it is extremely vulnerable to obstacles and requires very narrow (highly directional) beams for highly focused energy radiation. The main task of THz medium access control (MAC) protocol is not channel access collision avoidance; instead, it is to coordinate all the one-hop neighbors for scheduled, antenna-aligned line-of-sight communications. This study aims to build an intelligent MAC scheme for highly mobile Terahertz airborne networks (TANs). Our TAN MAC design has three features as follows: (1) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Spatio-temporal TAN state learning:</i> We will build a predictive network state estimation model through deep learning and generative adversarial network (GAN). Based on the predicted node/link status, all the one-hop neighbors can prepare well for the antenna alignment and THz channel scheduling. (2) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Accurate, two-level MAC operation control:</i> we propose to use nested deep reinforcement learning (DRL) with outer/inner policy loops for high-/low-level action determination: The outer loop determines the high-level, coarse actions (such as antenna codebook selection); the inner loop determines the low-level, fine actions (such as individual beam control) under the selected high-level action. (3) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TAN-specific, comprehensive MAC behavior control:</i> Based on the above deep neighbor adaptation (DNA) model, we design a complete TAN MAC protocol that considers the routing context and dynamic network topology. Our simulations demonstrate the smooth, high-rate THz communications in MAC layer with resilient RF links under high node mobility.

A proactive Medium Access Control (MAC) for finite-sized machine-to-machine (M2M) communication networks

In order to establish communication links among different communication devices or machines, the Medium Access Control (MAC) has to schedule the simultaneous transmissions by the contending nodes to constrain the probability of outage at each receiver. An efficient channel access scheme should be able to schedule the highest number of concurrent transmissions while being easy to implement with minimal coordination between the contending nodes.The existing MAC schemes provide network-wide solutions without adaptiveness, such as in existing guard zone-based solutions. On the other hand, an adaptive channel access scheme is proposed in this paper, which instead of declaring a network-wide fixed guard zone employs each interferer’s Transmitter–Receiver (Tx–Rx) separation to conclude its incorporation in the scheduled transmissions. The suggested scheme warrants the spatial separation among the scheduled links by suppressing the dominant interferers. The proposed MAC design functions approximately as good as the centralized, otherwise infeasible, joint scheduling and power control algorithm. In addition, the recommended scheme has proved its strength by outperforming both Carrier Sense Multiple Access (CSMA) and fix-sized guard zone schemes by significant margins under strict outage constraints and high contention density. The proposed scheme provided up to 100% and 60% better transmission capacity when compared with CSMA and fix-sized guard zone-based scheme, respectively. This paper also presents the closed-form results for the optimal guard zone size multiplier and the corresponding throughput capacity in terms of various network variables, such as contention density, outage constraint, Tx–Rx separation, network’s path loss exponent and spreading factor.

On the Efficiency of Multi-Beam Medium Access for Millimeter-Wave Networks

The need of highly directional communications at mmWave band introduces high overhead for beam training and alignment, which also makes the medium access control (MAC) a grand challenge. However, the need of supporting highly directional multiple beams between transmitters and receivers makes the MAC design even harder. To harvest the gain of multi-beam mmWave communications, which benefits not only from the large bandwidth of mmWave spectrum but also the diversity of concurrent multi-user multi-beam transmissions, this paper studies the medium access control (MAC) layer related issues in multi-beam mmWave networks, including (1) efficient multi-beam training schemes to enable lower overhead thus faster AP association and beam alignment, (2) block-sparse mmWave channel estimation in different beam resolutions, and (3) effective concurrent radio resource allocation to facilitate better multi-user multi-beam transmissions. Simulation results demonstrate that the proposed schemes outperform existing techniques in improving the efficiency of mmWave communications thus achieving significantly higher network performances. To our best knowledge, we are the first to comprehensively consider both efficient training for beam alignment and resource scheduling in the MAC design to enable highly directional multi-user multi-beam concurrent transmissions in a mmWave network.

Parallel Access Scheme for Wireless and Power Line Dual-Connection Communication

Hybrid communication of power line and wireless can improve the performance without dedicated communication lines and meet the requirements of in-vehicle communication. Aiming at the medium access control (MAC) design of dual-connection architecture, we propose a parallel access scheme for power line and wireless hybrid communication suitable for parallel diversity transmission, and establish transmission and collision probability equations on the basis that the two channel conditions are consistent. Further, the influences of the carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA) on the performance of the parallel access scheme are analyzed. Based on numerical results, it is shown that the proposed scheme can significantly improve the performance of throughput and delay when compared to power line and wireless network alone.

A Fair and Cooperative MAC Protocol for Heterogeneous Cognitive Radio Enabled Vehicular Ad-Hoc Networks

Advancements in intelligent transportation necessitate a dependable medium access control (MAC) protocol to enable high-priority safety broadcasts. Implementing cognitive radio-based vehicular ad-hoc networks (CR-VANETs) alleviates the significant growth in spectrum demand. The architecture must deploy multiple networks to make CR-VANET viable; however, the MAC design is a substantial challenge. The hardware-limited vehicles have varied characteristics and do not attain the same performance when provided with equal resources, posing a fairness concern. The resource allocation should balance two conflicting objectives: performance should be increased, prioritizing a few users under better conditions, and fairness among users should be emphasized, which reduces the overall performance. This paper presents a Fair and Cooperative MAC protocol for heterogeneous CR-VANETs (FCCR-MAC) to find this balance. In the event of a primary user appearance, cooperation allows pro-active channel switching. In FCCR-MAC, mode selection and retransmission of unsuccessful broadcasts are enabled by including additional control signals. By assisting users in determining the identities of others, cooperation also improves the system’s fairness. Markov Chain and the Karush–Kuhn–Tucker (KKT) conditions are utilized to offer a unified mathematical explanation of the throughput versus fairness trade-off optimization problem. According to the findings, the FCCR-MAC protocol outperforms other protocols with better fairness.

Medium access control protocol design for wireless communications and networks review

&lt;p&gt;&lt;span&gt;Medium access control (MAC) protocol design plays a crucial role to increase the performance of wireless communications and networks. The channel access mechanism is provided by MAC layer to share the medium by multiple stations. Different types of wireless networks have different design requirements such as throughput, delay, power consumption, fairness, reliability, and network density, therefore, MAC protocol for these networks must satisfy their requirements. In this work, we proposed two multiplexing methods for modern wireless networks: Massive multiple-input-multiple-output (MIMO) and power domain non-orthogonal multiple access (PD-NOMA). The first research method namely Massive MIMO uses a massive number of antenna elements to improve both spectral efficiency and energy efficiency. On the other hand, the second research method (PD-NOMA) allows multiple non-orthogonal signals to share the same orthogonal resources by allocating different power level for each station. PD-NOMA has a better spectral efficiency over the orthogonal multiple access methods. A review of previous works regarding the MAC design for different wireless networks is classified based on different categories. The main contribution of this research work is to show the importance of the MAC design with added optimal functionalities to improve the spectral and energy efficiencies of the wireless networks.&lt;/span&gt;&lt;/p&gt;

Massive Access of Static and Mobile Users via Reconfigurable Intelligent Surfaces: Protocol Design and Performance Analysis

The envisioned wireless networks of the future entail the provisioning of massive numbers of connections, heterogeneous data traffic, ultra-high spectral efficiency, and low latency services. This vision is spurring research activities focused on defining a next generation multiple access (NGMA) protocol that can accommodate massive numbers of users in different resource blocks, thereby, achieving higher spectral efficiency and increased connectivity compared to conventional multiple access schemes. In this article, we present a multiple access scheme for NGMA in wireless communication systems assisted by multiple reconfigurable intelligent surfaces (RISs). In this regard, considering the practical scenario of static users operating together with mobile ones, we first study the interplay of the design of NGMA schemes and RIS phase configuration in terms of efficiency and complexity. Based on this, we then propose a multiple access framework for RIS-assisted communication systems, and we also design a medium access control (MAC) protocol incorporating RISs. In addition, we give a detailed performance analysis of the designed RIS-assisted MAC protocol. Our extensive simulation results demonstrate that the proposed MAC design outperforms the benchmarks in terms of system throughput and access fairness, and also reveal a trade-off relationship between the system throughput and fairness.

A Collision Avoidance Based Energy Efficient Medium Access Control Protocol for Clustered Underwater Wireless Sensor Networks

Underwater Wireless Sensor Networks (UWSNs) are typically deployed in energy constrained environments where recharging energy sources and replacing batteries are not viable. This makes energy efficiency in UWSNs a crucial directive to be followed during Medium Access Control (MAC) design. Multiplexing and scheduling based protocols are not ideal for UWSNs because of their strict synchronization requirements, longer latencies and constrained bandwidth. This paper presents the development and simulation analysis of a novel cross-layer communication based MAC protocol called Energy Efficient Collision Avoidance (EECA) MAC protocol. EECA-MAC protocol works on the principle of adaptive power control, controlling the transmission power based on the signal strength at the receiver. EECA-MAC enhances the conventional 4-way handshake to reduce carrier sensing by implementing an enhanced Request to Send (RTS) and Clear to Send (CTS) handshake and an improved back-off algorithm. Simulation analysis shows that the measures taken to achieve energy efficiency have a direct effect on the number of packet retransmissions. Compared to the Medium Access with Collision Avoidance (MACA) protocol, EECA-MAC shows a 40% reduction in the number of packets that are delivered after retransmissions. This reduction, coupled with the reduced signal interference, results in a 16% drop in the energy utilized by the nodes for data transmission.

Energy-Efficient Collision Avoidance MAC Protocols for Underwater Sensor Networks: Survey and Challenges

The Medium Access Control (MAC) layer protocol is the most important part of any network, and is considered to be a fundamental protocol that aids in enhancing the performance of networks and communications. However, the MAC protocol’s design for underwater sensor networks (UWSNs) has introduced various challenges. This is due to long underwater acoustic propagation delay, high mobility, low available bandwidth, and high error probability. These unique acoustic channel characteristics make contention-based MAC protocols significantly more expensive than other protocol contentions. Therefore, re-transmission and collisions should effectively be managed at the MAC layer to decrease the energy cost and to enhance the network’s throughput. Consequently, handshake-based and random access-based MAC protocols do not perform as efficiently as their achieved performance in terrestrial networks. To tackle this complicated problem, this paper surveys the current collision-free MAC protocols proposed in the literature for UWSNs. We first review the unique characteristic of underwater sensor networks and its negative impact on the MAC layer. It is then followed by a discussion about the problem definition, challenges, and features associated with the design of MAC protocols in UWANs. Afterwards, currently available collision-free MAC design strategies in UWSNs are classified and investigated. The advantages and disadvantages of each design strategy along with the recent advances are then presented. Finally, we present a qualitative comparison of these strategies and also discuss some possible future directions.

Distribution of Safety Messages Using Mobility-Aware Multi-Hop Clustering in Vehicular Ad Hoc Network

Reliability and security when distributing safety messages among vehicles in an extremely mobile environment are prominent issues in Vehicular Ad-Hoc Networks (VANETs). In VANET, data transfer becomes challenging because of inherent features such as excessive speed, geographically constrained topologies, unsteady communication links, diversity in the capacity of the channel, etc. A major challenge in the multi-hop framework is maintaining and building a path under such a rigid environment. With VANET, potency in the traffic safety applications has performed well because of the proper design of medium access control (MAC) protocols. In this article, a protocol is proposed pertaining to the distribution of safety messages named mobility-aware multi-hop clustering-based MAC (MAMC-MAC) to accomplish minimum communication overhead, high reliability, and delivery of safety messages in real-time environments. MAMC-MAC has the ability to establish clustering-based multi-hop sequence using the time-division multiple access (TDMA) technique. The protocol was specially developed for highway outlines to achieve network enhancement and efficient channel usage and guarantees integrity among the vehicles. The performance of the proposed protocol is evaluated using Network Simulator (NS-2), and it demonstrates its superiority over various standard protocols in terms of a number of quality-of-service (QoS)-based parameters. The criteria to select and assess these parameters are their sensitivity and importance to the safety-based applications they provide.

A mobility‐aware cluster‐based MAC protocol for radio‐ frequency energy harvesting cognitive wireless sensor networks

Cognitive wireless sensor networks (CWSN) are severely energy constrained and radio frequency (RF) wireless energy harvesting (RFWEH) has been shown to improve the network lifetime. In many CWSN applications, node mobility imposes challenges owing to changing network topology. Therefore, the design of a new medium access control (MAC) protocol that can handle node mobility as well as energy harvesting is required. A cluster-based multihop MAC protocol (RMAC-M) is proposed that incorporates RF energy harvesting in a mobility-aware CWSN. Our protocol selects cluster heads using an algorithm based on an R-factor parameter consisting of residual node energy, residual node data and node speed, with appropriate weights. It then transmits data packages using a multitier super cluster head routing mechanism without the need for neighbour discovery. The multitier clustering and RFWEH mechanisms boost the energy performance of the network, increasing its lifetime. On the other hand, time slots allocated for RFWEH increase delay, thereby affecting system latency. Owing to its unique nature, the proposed algorithm has no comparable protocols in the literature. For the sake of completeness, RMAC-M is compared with well-known MAC protocols such as LEACH-M and KoNMAC that do not have energy harvesting or mobility features. Simulation results show that the proposed protocol increases the lifetime of the CWSN nodes substantially, promising a self-sustainable network in terms of energy. Furthermore, despite the allocation of time slots for energy harvesting, critical network parameters such as throughput, packet loss and average delay remain within target levels.

A Study on the Wireless Body Area Network MAC Protocol Using Dynamic Superframe for e-Health IoT

One of the most remarkable applications of the Internet of Things is health monitoring. Wireless body area networks (WBANs) consist of several body sensors implanted in or place on a human body and a coordinator. One of the essential issues of WBANs is the design of Medium Access Control (MAC) protocol to improve system efficiency. In this paper, we modify the IEEE 802.15.4 standard MAC superframe structure and propose an energy-efficient MAC protocol for WBANs in the e-Health Internet of Things (IoT) systems. In this scheme, the time slots are divided into mini-slots. The lengths of the contention access period and the contention free period are both variable. By using this mechanism, the utility of time slots can be considerably increased.

AI-Assisted MAC for Reconfigurable Intelligent-Surface-Aided Wireless Networks: Challenges and Opportunities

Recently, significant research attention has been devoted to the study of reconfigurable intelligent surfaces (RISs), which are capable of reconfiguring the wireless propagation environment by exploiting the unique properties of metamaterials-based integrated large arrays of inexpensive antennas. Existing research demonstrates that RISs significantly improve physical layer performance, including wireless coverage, achievable data rate, and energy efficiency. However, the medium access control (MAC) of multiple users accessing an RIS-enabled channel is still in its infancy, while many open issues remain to be addressed. In this article, we present four typical RIS-aided multi-user scenarios with special emphasis on the MAC schemes. We then propose and elaborate on centralized, distributed, and hybrid artificial-in-telligence-assisted MAC architectures in RIS-aid-ed multi-user communications systems. Finally, we discuss some challenges, perspectives, and potential applications of RISs as they are related to MAC design.

Energy-Efficient MAC for Cellular IoT: State-of-the-Art, Challenges, and Standardization

In the modern world, the connectivity-as-we-go model is gaining popularity. Internet-of-Things (IoT) envisions a future in which human beings communicate with each other and with devices that have identities and virtual personalities, as well as sensing, processing, and networking capabilities, which will allow the developing of smart environments that operate with little or no human intervention. In such IoT environments, that will have battery-operated sensors and devices, energy efficiency becomes a fundamental concern. Thus, energy-efficient (EE) connectivity is gaining significant attention from the industrial and academic communities. This work aims to provide a comprehensive state-of-the-art survey on the energy efficiency of medium access control (MAC) protocols for cellular IoT. we provide a detailed discussion on the sources of energy dissipation at the MAC layer and then propose solutions. In addition to reviewing the proposed MAC designs, we also provide insights and suggestions that can guide practitioners and researchers in designing EE MAC protocols that extend the battery life of IoT devices. Finally, we identify a range of challenging open problems that should be solved for providing EE MAC services for IoT devices, along with corresponding opportunities and future research ideas to address these challenges.

FMCW Radar Network: Multiple Access and Interference Mitigation

With the increasing proliferation of radars on vehicles, interference among vehicular radars is becoming a serious issue. In this work, we consider a frequency modulated continuous wave (FMCW) radar network with coherent radar interference where all radars adopt the same chirp slopes. Four asynchronous non-cooperative media access control (MAC) protocols are used for mutual radar interference mitigation. We propose two cross-layer performance metrics - multiple access capacity and probability of target misdetection to quantify the network performance under each MAC protocol. Based on our analysis and extensive simulations, we find the pure random access achieves a very poor trade-off between multiple access capacity and probability of target misdetection. However, such a trade-off can be significantly improved by frequency hopping and phase coding. This shows that proper MAC protocols can achieve very good performance even without synchronization and coordination. We describe new insights behind such gains that can be valuable for FMCW radar MAC design.

Huffman Coding and Multi-Generation Mixing Assisted Network Coding Based MAC for QoS-Centric Secure Data Communication over MANETs

The exponential rise in wireless transmission has gained widespread attention to meet major mobile communication purposes including, Internet of Things (IoT) and Machine-to-Machine (M2M) communications. Mobile Ad-hoc Network (MANET) has emerged as one of the most viable solution to meet aforesaid mobile communication purposes; however, being decentralized and infrastructure-less network it undergoes adversaries including dynamic topology and security breaches due to malicious node attachment during routing. On the contrary, data security and allied Quality-of-Service (QoS) provision are inevitable in NextGen communication systems. Unlike routing-based security measures, Medium Access Control (MAC) based approaches are found more effective for MANETs. However, most of the classical MAC designs either address QoS or security as standalone objective. Unlike existing MAC solutions, in this paper a state-of-art novel Huffman Coding and Multi-Generation Mixing (MGM) assisted random linear network model-based MAC design (HM2-MAC) is proposed for MANET. Realizing the robustness of the network coding algorithms towards reliable, secure and error-free multicast transmission, we designed HM2-MAC in such manner that Huffman coding helps securing the source data packets, while MGM concept enables reduction in redundant packets to make overall communication resource efficient and secure. Unlike redundant packet-per-generation, MGM concept helps in reducing redundant transmission and hence achieves resource efficiency. Since, in HM2-MAC model the coefficient matrix used to encode the data is known only to the sink, no intermediate node can decode it or can pollute it. It makes multicast transmission more secure over MANET. Additionally, the use of iterative buffer flush technique preserves resources or buffer to accommodate more data for transmission and hence higher throughput. Noticeably, error sensitive packetization and MGM control strengthens our proposed model to retain optimal performance. HM2-MAC has been applied as a sub-layer of native IEEE 802.11 MAC and hence retains backward compatibility towards real-world implementation. MATLAB based simulation revealed that our proposed HM2-MAC protocol achieved almost 99.6% throughput even under varying link-loss patterns, which reveals its robustness to ensure QoS delivery with secure data transmission in MANET.

Dual-Radio-Assisted (DRA) MAC Protocols for Distributed Terahertz Networks

Terahertz (THz) communication is envisioned as one of the key technologies to satisfy the high data rate demand of intelligent 6G networks. However, directional transmissions, as well as the peculiarities of the THz band, pose challenges on medium access control (MAC) design. In this paper, a dual-radio-assisted MAC protocol supporting concurrent transmission is proposed, in which 2.4/5 GHz omnidirectional radio is utilized for control signaling, while THz beamforming is adopted for data transmissions. The request-to-send (RTS-GHz)/test-to-transmit (TTT-THz) handshake is adopted for initial link establishment. Furthermore, the network table is constructed at each node recording receiver-oriented network allocation vector (RNAV) value, angle-of-departure (AoD) of DATA, and angle-of-arrival (AoA) of RTS-GHz. The RNAV record enables concurrent transmission without collision. The record of the first two dominant AoA paths alleviates the LoS blockage problem. The AoD record further decreases the link association delay by replacing RTS-THz with RTS-GHz. Network performances on the protocol are analytically and numerically investigated. Results indicate that the proposed DRA-MAC protocol with AoD memory can achieve 88.2%, 51.6%, and 50% improvement in average link delay, throughput, and LoS blockage alleviation respectively, compared with existing THz MAC protocols.

Sensing and Communication Co-Design for Status Update in Multiaccess Wireless Networks

The sensing and communication layers are both integral parts of the Internet-of-Things. Most of recent studies on sensory status update treat the information sensing and sensory data communication problems separately (i.e., a decoupled approach) and optimize specific latency metrics such as age of information relying on simplified models of communication networks or sensory traffic. In this paper, we propose a deeply integrated sensing and communication scheduling (S2) framework based on status-error-triggered update, focusing specifically on multiaccess wireless networks. We first analyze a motivating example consisting of two-state Markov sensors, showing that when both optimized, S2 outperforms the decoupled approach significantly. For sensors with random-walk state transitions, the closed-form Whittle's index with arbitrary status tracking error functions is presented and the indexability is established. Furthermore, a mean-field approach is applied such that the decentralized status update medium access control design is solved explicitly, for both homogeneous nodes and heterogeneous nodes in terms of status transition behaviors. According to the numerical results, the performance of the proposed S2 scheme is close to the optimum and better than the decoupled approach. In addition, a potential application of dynamic Channel State Information (CSI) update is presented, with CSI generated by a commercial ray-tracing simulator.