Boris Bellalta

IEEE 802.11AH: the WiFi approach for M2M communications

M2M communications are positioned to be one of the fastest growing technology segments in the next decade. Sensor and actuator networks connect communication machines and devices so that they automatically transmit information, serving the growing demand for environmental data acquisition. The IEEE 802.11ah Task Group is working on a new standard to address the particular requirements of M2M networks: a large number of power-constrained stations; a long transmission range; small and infrequent data messages; low data rates; and a non-critical delay. This article explores the key features of this new standard, especially those related to the reduction of energy consumption in the medium access control layer. Given these requirements, a performance assessment of IEEE 802.11ah in four common M2M scenarios, i.e. agriculture monitoring, smart metering, industrial automation, and animal monitoring, is presented.

Low energy operation in WSNs: A survey of preamble sampling MAC protocols

The limited energy resources of sensor nodes are among the most important constraints in Wireless Sensor Networks (WSNs). Consequently, the Medium Access Control (MAC) layer design is crucial, due to its influence on the transceiver, which is the most energy-consuming component of a sensor node. Among the different MAC protocols designed for WSNs, preamble sampling techniques provide extremely low energy consumption at low loads and have a notably simple operation and a lack of synchronisation requirements, which are characteristics that are especially appealing to WSNs. In this work, a survey of the different types of MAC protocols designed for WSNs is presented with a special focus on preamble sampling MAC protocols. The aim of this work is to give a detailed overview and classification of the most relevant preamble sampling MAC protocols, being motivated by the extremely large number of MAC protocols designed for WSNs in recent years. Moreover, a simple set of guidelines for matching the most suitable MAC protocol category to a given application is provided in this work.

IEEE 802.11ax: High-efficiency WLANS

IEEE 802.11ax-2019 will replace both IEEE 802.11n-2009 and IEEE 802.11ac-2013 as the next high-throughput WLAN amendment. In this article, we review the expected future WLAN scenarios and use cases that justify the push for a new PHY/MAC IEEE 802.11 amendment. After that, we overview a set of new technical features that may be included in the IEEE 802.11ax-2019 amendment, and describe both their advantages and drawbacks. Finally, we discuss some of the network-level functionalities that are required to fully improve the user experience in next-generation WLANs and note their relation with other ongoing IEEE 802.11 amendments.

On the Performance of Packet Aggregation in IEEE 802.11ac MU-MIMO WLANs

Multi-user spatial multiplexing combined with packet aggregation can significantly increase the performance of Wireless Local Area Networks (WLANs). In this letter, we present and evaluate a simple technique to perform packet aggregation in IEEE 802.11ac MU-MIMO (Multi-user Multiple Input Multiple Output) WLANs. Results show that in non-saturation conditions both the number of active stations (STAs) and the queue size have a significant impact on the system performance. If the number of STAs is excessively high, the heterogeneity of destinations in the packets contained in the queue makes it difficult to take full advantage of packet aggregation. This effect can be alleviated by increasing the queue size, which increases the chances of scheduling a large number of packets at each transmission, hence improving the system throughput at the cost of a higher delay.

Performance Evaluation of IEEE 802.11p-Enabled Vehicular Video Surveillance System

Prospective IEEE 802.11p-based vehicular surveillance system, where video from the vehicle on-board camera is transmitted to the management center, is considered. Multi-hop transmission from the vehicle to the nearest roadside unit and then - via other roadside units - to the gateway is addressed. In this letter we assess the feasibility of such system by analyzing the video end-to-end distortion for a target vehicle, located several hops away from the gateway, when it is alone or there are also other vehicles transmitting video. We demonstrate the importance of dynamic adaptation of the video bit rate of each vehicle depending on the number and positions of the participating vehicles.

Game theory for energy efficiency in Wireless Sensor Networks

In the area of Wireless Sensor Networks (WSNs), improving energy efficiency and network lifetime is one of the most important and challenging issues. Most of the considered WSNs are formed by nodes with limited resources, in which each node plays dual rule of both sensing the environment and relaying traffic to the sink from other nodes. On the one hand, the nodes need to stay alive as long as possible by achieving energy efficiency. On the other hand, they have to provide the required service. This conflict of interest makes game theory very useful in WSNs. Moreover, nodes usually have to make decisions with limited information about the state of the network. Game theory has been used recently in a remarkable amount of research in this area. In this survey, we review the most recent papers about using game theory in WSNs to achieve a trade-off between maximizing the network lifetime and providing the required service. The paper contains a complete taxonomy of games applied to this specific research problem. It summarizes and compares the different published proposals along with tables and statistical charts showing in which domains game theory has been applied recently. Overall, the paper will give to researchers a clear view of the newest trends in this research area, underlining its main challenges and hopefully fostering discussions and new research directions.

CSMA with Enhanced Collision Avoidance: A Performance Assessment

CSMA with Enhanced Collision Avoidance (CSMA/ECA) uses a deterministic backoff after successful transmissions to significantly reduce the number of collisions. This paper assesses by means of simulations the throughput and conditional collision probability obtained from a single-hop ad-hoc network using CSMA/ECA. A comparison with the legacy CSMA/CA reveals that the proposed protocol outperforms the legacy one in all considered scenarios. Specifically, it is shown that CSMA/ECA presents advantages for both rigid and elastic flows.

A low power listening MAC with scheduled wake up after transmissions for WSNs

This work presents a new MAC protocol for WSNs that combines an unscheduled channel access, based on lowpower listening, with an opportunistic scheduled wake up after transmissions mechanism. The proposed MAC provides a good tradeoff between energy consumption, complexity and performance in terms of throughput and delay. It achieves the benefits of scheduled MAC protocols without the cost of maintaining and sharing the schedule, as well as the low consumption and simple operation of unscheduled MAC protocols.

MU-MIMO MAC Protocols for Wireless Local Area Networks: A Survey

As wireless devices boom and bandwidth-hungry applications (e.g., video and cloud uploading) get popular, todays wireless local area networks (WLANs) become not only crowded but also stressed at throughput. Multiuser multiple-input-multiple-output (MU-MIMO), an advanced form of MIMO, has gained attention due to its huge potential in improving the performance of WLANs. This paper surveys random access-based medium access control (MAC) protocols for MU-MIMO-enabled WLANs. It first provides background information about the evolution and the fundamental MAC schemes of IEEE 802.11 Standards and Amendments, and then identifies the key requirements of designing MU-MIMO MAC protocols for WLANs. After this, the most representative MU-MIMO MAC proposals in the literature are overviewed by benchmarking their MAC procedures and examining the key components, such as the channel state information acquisition, decoding/precoding, and scheduling schemes. Classifications and discussions on important findings of the surveyed MAC protocols are provided, based on which, the research challenges for designing effective MU-MIMO MAC protocols, as well as the envisaged MACs role in the future heterogeneous networks, are highlighted.

Next generation IEEE 802.11 Wireless Local Area Networks: Current status, future directions and open challenges

A new generation of Wireless Local Area Networks (WLANs) will make its appearance in the market in the forthcoming years based on the amendments to the IEEE 802.11 standards that have recently been approved or are under development. Examples of the most expected ones are IEEE 802.11aa (Robust Audio Video Transport Streaming), IEEE 802.11ac (Very-high throughput at < 6 GHz), IEEE 802.11af (TV White Spaces) and IEEE 802.11ah (Machine-to-Machine communications) specifications. The aim of this survey is to provide a comprehensive overview of these novel technical features and the related open technical challenges that will drive the future WLAN evolution. In contrast to other IEEE 802.11 surveys, this is a use case oriented study. Specifically, we first describe the three key scenarios in which next-generation WLANs will have to operate. We then review the most relevant amendments for each of these use cases focusing on the additional functionalities and the new technologies they include, such as multi-user MIMO techniques, groupcast communications, dynamic channel bonding, spectrum databases and channel sensing, enhanced power saving mechanisms and efficient small data transmissions. We also discuss the related work to highlight the key issues that must still be addressed. Finally, we review emerging trends that can influence the design of future WLANs, with special focus on software-defined MACs and the internet-working with cellular systems.