MAC Layer Perspective Research Articles

Enabling Energy Harvesting-Based Wi-Fi System for an e-Health Application: A MAC Layer Perspective.

The adverse impacts of using conventional batteries in the Internet of Things (IoT) devices, such as cost-effective maintenance, numerous battery replacements, and environmental hazards, have led to an interest in integrating energy harvesting technology into IoT devices to extend their lifetime and sustainably effectively. However, this requires improvements in different IoT protocol stack layers, especially in the MAC layer, due to its high level of energy consumption. These improvements are essential in critical applications such as IoT medical devices. In this paper, we simulated a dense solar-based energy harvesting Wi-Fi network in an e-Health environment, introducing a new algorithm for energy consumption mitigation while maintaining the required Quality of Service (QoS) for e-Health. In compliance with the upcoming Wi-Fi amendment 802.11be, the Access Point (AP) coordination-based optimization technique is proposed, where an AP can request dynamic resource rescheduling along with its nearby APs, to reduce the network energy consumption through adjustments within the standard MAC protocol. This paper shows that the proposed algorithm, alongside using solar energy harvesting technology, increases the energy efficiency by more than 40% while maintaining the e-Health QoS requirements. We believe this research will open new opportunities in IoT energy harvesting integration, especially in QoS-restricted environments.

Toward End-to-End, Full-Stack 6G Terahertz Networks

Recent evolutions in semiconductors have brought the terahertz band in the spotlight as an enabler for terabit-per-second communications in 6G networks. Most of the research so far, however, has focused on understanding the physics of terahertz devices, circuitry and propagation, and on studying physical layer solutions. However, integrating this technology in complex mobile networks requires a proper design of the full communication stack, to address link- and system-level challenges related to network setup, management, coordination, energy efficiency, and end-to-end connectivity. This paper provides an overview of the issues that need to be overcome to introduce the terahertz spectrum in mobile networks, from a MAC, network and transport layer perspective, with considerations on the performance of end-to-end data flows on terahertz connections.

Performance Analysis of Grant-Free Multiple Access for Supporting Sporadic Traffic in Massive IoT Networks

Grant-free multiple access (GFMA) protocol has been regarded as a key element to support sporadic traffic generated from massive internet-of-things (IoT) networks. In GFMA protocol, each IoT device transmits data packets without grant from a base station (BS) via pre-reserved uplink resources. Packet collisions inherently occur when multiple IoT devices transmit packets by using the same radio resource, but the collision effect can be alleviated with multi-packet reception (MPR) capability of the BS. Since a number of studies have focused on improving the physical layer performance such as bit error rate, they may be hard to provide intuitions from the MAC layer perspective when a number of IoT devices sporadically generate uplink packets and attempt the GFMA. In this paper, we thoroughly investigate the GFMA from the MAC layer perspective. We provide an analytical framework based on a Markov chain to capture the performance of the GFMA in terms of packet transmission success probability, ergodic throughput, and access delay. Through simulations, we validate our analytical framework and verify the necessity of adopting MPR technique for supporting a massive number of IoT devices generating sporadic traffic.

Analysis of TCP-unfairness from MAC Layer Perspective in Wireless Ad-hoc Networks

In Ad-hoc networks every single node or station takes the responsibility to forward the data packets from the nodes that lie in the range with them. This additional routing responsibility might lead to performance degradation in some cases. Moreover, it is also reported that TCP which is designed for wired networks exhibit poor performance in terms of throughput and fairness in ad-hoc networks. Attempts to alleviate this issue included solutions from both TCP and MAC layer protocol modifications. This work aims at in-depth analysis of MAC level solutions (basic 802.11, 802.11 with RTS/CTS and Collision Detection Mechanism Based-MAC) to address TCP unfairness problem in 802.11-based multi-hop networks. A set of simulation based experiments are conducted and their observations are analyzed using metrics like throughput, goodput and loss probability. The metric loss probability is taken to investigate the protocols both from the perspective of congestion and collision i.e. the impact of congestion window and contention procedure on the end-to-end performance. The results obtained from the simulation revealed the inefficiency of the CDMB-MAC in the scenarios where hidden and exposed terminals do not exist. Further when TCP congestion window is set to 1 the basic 802.11 MAC is found sufficient to provide higher throughput with better fairness among the TCP connections but when TCP congestion window size is increased to 32 the 802.11 MAC with RTS/CTS scheme gives better performance. Added to this all the three MAC protocols fail in the scenario where the source and destination of a connection lie in the transmission ranges of destination and source of other connections. Therefore it can be concluded that it is indispensable to design an adaptive MAC protocol that could provide Fairness among TCP connections in all scenarios.

Stochastic Control of Relay Channels With Cooperative and Strategic Users

This paper studies node cooperation in a wireless network from the MAC layer perspective. A simple relay channel with a source, a relay, and a destination node is considered where the source can transmit a packet directly to the destination or transmit through the relay. The tradeoff between average energy and delay is studied by posing the problem as a stochastic dynamical optimization problem. The following two cases are considered: 1) nodes are cooperative and information is decentralized, and 2) nodes are strategic and information is centralized. With decentralized information and cooperative nodes, a structural result is proven that the optimal policy is the solution of a Bellman-type fixed-point equation over a time invariant state space. For specific cost functions reflecting transmission energy consumption and average delay, numerical results are presented showing that a policy found by solving this fixed-point equation outperforms conventionally used time-division multiple access (TDMA) and random access (RA) policies. When nodes are strategic and information is common knowledge, it is shown that cooperation can be induced by exchange of payments between the nodes, imposed by the network designer such that the socially optimal Markov policy corresponding to the centralized solution is the unique subgame perfect equilibrium of the resulting dynamic game.

Successive Interference Cancellation: Carving Out MAC Layer Opportunities

Successive interference cancellation (SIC) is a PHY capability that allows a receiver to decode packets that arrive simultaneously. While the technique is well known in communications literature, emerging software radio platforms are making practical experimentation feasible. This motivates us to study the extent of throughput gains possible with SIC from a MAC layer perspective and scenarios where such gains are worth pursuing. We find that contrary to our initial expectation, the gains are not high when the bits of interfering signals are not known a priori to the receiver. Moreover, we observe that the scope for SIC gets squeezed by the advances in bitrate adaptation. In particular, our analysis shows that interfering one-to-one transmissions benefit less from SIC than scenarios with many-to-one transmissions (such as when clients upload data to a common access point). In view of this, we develop an SIC-aware scheduling algorithm that employs client pairing and power reduction to extract the most gains from SIC. We believe that our findings will be useful guidelines for moving forward with SIC-aware protocol research.

Exploiting Cooperative Advantages in Slotted ALOHA Random Access Networks

In cooperative systems, users achieve spatial diversity and multihop gains by transmitting packets over multiple independent fading paths provided by their partners. Most previous works on cooperative communications focus on the physical layer aspects such as coding, modulation, and transceiver signal processing techniques. In this work, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit cooperative gains in random access networks. Based on the conventional slotted ALOHA protocol, we propose a simple cooperative transmission mechanism for a two-user cooperative pair. We derive the two-user stability region of the proposed system and show the improvements compared to noncooperative systems. The benefits can be attributed to both physical layer cooperation, where users with good channels may relay for those with bad channels, and MAC layer cooperation, where system parameters can be chosen to enhance cooperation and reduce competition. Then, we extend the proposed strategy to a finite-user system that consists of multiple cooperative pairs. By treating each pair as a single transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

Cooperative MAC Design in Multi-hop Wireless Networks: Part I: When Source and Destination are within the Transmission Range of Each Other

Cooperative communication is regarded as a promising technology in future 5G wireless networks to enhance network performance by exploiting time and/or space diversity via distributed terminals. In this paper, we propose a cooperative medium access protocol which addresses three key aspects of cooperative communications from MAC layer perspective, namely, when to cooperate, whom to cooperate with and how to protect ongoing cooperative transmissions. To further improve the protocol performance in dense networks, three techniques are investigated to avoid potential collision among multiple contending relays. Both analysis and simulation results demonstrate that significant improvement in terms of throughput and packet delivery ratio can be achieved by the proposed cooperative protocol.

A Cross-Layer Approach to Heterogeneous Multi-User Diversity with Link Adaptation

Multi-user diversity (MUD) scheduling is based on the idea that access to the channel should be given to users with better channel state. In a system with many users whose channels vary independently, such strategy maximizes the probability that the channel of the scheduled user is near its peak. Consequently, the total ergodic capacity of the system is maximized. However, from a network point of view, performance is usually evaluated in terms of average throughput and average delay rather than ergodic capacity and fairness. Furthermore, information-theoretic rates are not achievable at the PHY layer and more practical solutions must be considered. In this paper the MUD problem is approached from a MAC layer perspective and the throughput maximal MUD scheduling policy, i.e., the policy that maximizes the total average throughput is investigated. We also study the average throughput region and show the suitability of optimal information-theoretic approaches in practical environments. The average throughput region is also contemplated in wireless networks where Heterogeneous multi-user diversity (HMUD) can be exploited. Finally, the average throughput region is related to the stability region and some average delay bounds for different ARQ mechanisms are provided.

A Cross-Layer Investigation for the Throughput Performance of CSMA/CA-Based WLANs With Directional Antennas and Capture Effect

In this paper, we develop a physical/medium-access-control (PHY/MAC) cross-layer analytical model to investigate the throughput performance of the wireless local-area network (WLAN) in a lossy wireless environment. From the PHY-layer perspective, the developed model incorporates the effects of capture and directional antennas, while from the MAC-layer perspective, our approach takes into account the carrier-sense multiple access with collision-avoidance (CSMA/CA) MAC protocol and the effect of the backoff process in the IEEE 802.11 WLAN. We derive explicit analytical expressions for the frame outage and capture probabilities of a directional antenna system in the presence of shadowing and Rayleigh fading. Applying this analysis, we can model the interaction between the PHY and MAC layers more accurately for the infrastructure-based WLAN. The numerical results show that our analytical model can approach that attained by simulations. The proposed cross-layer analytical model not only provides insights into the PHY layer impacts on the throughput of the CSMA/CA MAC protocol but also indicates to how directional antennas can improve the CSMA/CA-based WLAN in terms of antenna beamwidth and the number of radio transceivers.

QoS and energy efficiency in network wide broadcasting: A MAC layer perspective

In this paper we investigate the role of medium access control on the performance of network-wide real-time data broadcasting through flooding using three MAC protocols (IEEE 802.11, CPS, and MH-TRACE) in terms of QoS (packet delivery ratio, packet delay, and delay jitter) and energy dissipation. We conduct extensive simulations to evaluate the performance of network-wide broadcasting through flooding in the node density, traffic load, and network size/topology parameter space. The results of our study show that different MAC protocols produce better performance than the others in different parts of the parameter space. Thus, in designing network layer broadcast architectures, the characteristics of the medium access control layer should be given the utmost importance to ensure the satisfactory performance of the system.