Miquel Oliver

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.

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.

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.

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.

Towards a Collision-Free WLAN: Dynamic Parameter Adjustment in CSMA/E2CA

Carrier sense multiple access with enhanced collision avoidance (CSMA/ECA) is a distributed MAC protocol that allows collision-free access to the medium in WLANs. The only difference between CSMA/ECA and the well-known CSMA/CA is that the former uses a deterministic backoff after successful transmissions. Collision-free operation is reached after a transient state during which some collisions may occur. This paper shows that the duration of the transient state can be shortened by appropriately setting the contention parameters. Standard absorbing Markov chain theory is used to describe the behaviour of the system in the transient state and to predict the expected number of slots to reach the collision-free operation. The paper also introduces CSMA/E2CA, in which a deterministic backoff is used two consecutive times after a successful transmission. CSMA/E2CA converges quicker to collision-free operation and delivers higher performance than CSMA/ECA, specially in harsh wireless scenarios with high frame-error rates. The last part of the paper addresses scenarios with a large number of contenders. We suggest dynamic parameter adjustment techniques to accommodate a varying (and potentially high) number of contenders. The effectiveness of these adjustments in preventing collisions is validated by means of simulation.

Public Open Sensor Data: Revolutionizing Smart Cities

Local governments have decided to take advantage of the presence of wireless sensor networks (WSNs) in their cities to efficiently manage several applications in their daily responsibilities. The enormous amount of information collected by sensor devices allows the automation of several real-time services to improve city management by using intelligent traffic-light patterns during rush hour, reducing water consumption in parks, or efficiently routing garbage collection trucks throughout the city [1]. The sensor information required by these examples is mostly self-consumed by city-designed applications and managers.

A Simple Model of the IEEE 802.11 MAC Protocol with Heterogeneous Traffic Flows

We present a model of the IEEE 802.11 MAC protocol considering heterogeneous non-saturated traffic flows in a single-hop scenario. We validate the model comparing several performance measures with simulation results, showing the model accuracy and ability to catch the effect of flow multiplexing over the shared channel

Wireless Commons against the digital divide

Guifi is a community-based telecommunications network that originated in a rural area of the Spanish region of Catalonia. Guifi primarily uses unlicensed spectrum for its communications links, and its users create network nodes on a volunteer basis from state-of-the-art yet inexpensive off-the-shelf WiFi equipment. Guifis self-organizing community is governed by a Wireless Commons charter that views unlicensed spectrum as a public asset, which means that Guifi satisfies the definition of both an open Commons (an open network with free access) and a closed Commons (a self regulating community with a well defined charter). This article identifies key factors for the exponential growth and success of the WiFi network, which has put some rural areas in Catalonia well above European average for broadband penetration. Moreover, this article identifies the threats that Guifi faces as both an open and closed Commons, and explores what Guifi does or should do to mitigate them. These threats are referred to in literature as the “Tragedy of the Commons”. Finally, the article also considers possible consequences of Guifis intentions to expand its network with fiber connections.

Performance analysis of IEEE 802.11ac wireless backhaul networks in saturated conditions

According to the ongoing IEEE 802.11ac amendment, the wireless network is about to embrace the gigabit-per-second raw data rate. Compared with previous IEEE standards, this significant performance improvement can be attributed to the novel physical and medium access control (MAC) features, such as multi-user multiple-input multiple-output transmissions, the frame aggregation, and the channel bonding. In this paper, we first briefly survey the main features of IEEE 802.11ac, and then, we evaluate these new features in a fully connected wireless mesh network using an analytic model and simulations. More specifically, the performance of the MAC scheme defined by IEEE 802.11ac, which employs the explicit compressed feedback (ECFB) mechanism for the channel sounding, is evaluated. In addition, we propose an extended request-to-send/clear-to-send scheme that integrates the ECFB operation to compare with the IEEE 802.11ac-defined one in saturated conditions. The comparison of the two MAC schemes is conducted through three spatial stream allocation algorithms. A simple but accurate analytical model is derived for the two MAC schemes, the results of which are validated with simulations. The observations of the results not only reveal the importance of spatial stream allocations but also provide insight into how the newly introduced features could affect the performance of IEEE 802.11ac-based wireless mesh networks.