Jaume Barcelo

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.

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.

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.

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.

On the Interactions Between Multiple Overlapping WLANs Using Channel Bonding

Next-generation wireless local area networks (WLANs) will support the use of wider channels, which is known as channel bonding, to achieve higher throughput. However, because both the channel center frequency and the channel width are autonomously selected by each WLAN, the use of wider channels may also increase the competition with other WLANs operating in the same area for the available channel resources. In this paper, we analyze the interactions between a group of neighboring WLANs that use channel bonding and evaluate the impact of those interactions on the achievable throughput. A continuous-time Markov network model that is able to capture the coupled dynamics of a group of overlapping WLANs is introduced and validated. The results show that the use of channel bonding can provide significant performance gains, even in scenarios with a high density of WLANs, although it may also cause unfair situations in which some WLANs receive most of the transmission opportunities while others starve.

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.

Capacity Analysis of IEEE 802.11ah WLANs for M2M Communications

Focusing on the increasing market of the sensors and actuators networks, the IEEE 802.11ah Task Group is currently working on the standardization of a new amendment. This new amendment will operate at the sub-1GHz band, ensure transmission ranges up to 1 Km, data rates above 100 kbps and very low power operation. With IEEE 802.11ah, the WLANs will offer a solution for applications such as smart metering, plan automation, eHealth or surveillance. Moreover, thanks to a hierarchical signalling, the IEEE 802.11ah will be able to manage a higher number of stations (STAs) and improve the 802.11 Power Saving Mechanisms. In order to support a high number of STAs, two different signalling modes are proposed, TIM and Non-TIM Offset. In this paper we present a theoretical model to predict the maximum number of STAs supported by both modes depending on the traffic load and the data rate used. Moreover, the IEEE 802.11ah performance and energy consumption for both signalling modes and for different traffic patterns and data rates is evaluated. Results show that both modes achieve similar Packet Delivery Ratio values but the energy consumed with the TIM Offset is, in average, 11.7% lower.

Fairness and Convergence of CSMA with Enhanced Collision Avoidance (ECA)

This paper presents CSMA/ECA, which combines the efficiency of reservation-based protocols and the simplicity of random access mechanisms. The maximum efficiency of CSMA/CA with optimal parameter adjustment is easily exceeded by CSMA/ECA, even when fixed parameters are used by the latter. CSMA/ECA stations fairly coexist with legacy CSMA/CA and increase the portion of time that is devoted to successful transmissions while decreasing the number of collisions and empty slots. The proposed mechanism initially behaves as a CSMA/CA network, but it progressively converges to a collision-free deterministic operation. The convergence process can be modelled as a Markov Chain to assess the duration of the transitory phase.

Wireless open metropolitan area networks

IEEE 802.11 technologies allow the deployment of metropolitan access networks. This paper details the reasons for making these networks open to several service providers. The sharing of the wireless access network fosters competition and ultimately benefits the users. The second part of the paper describes the available technologies that allow such infrastructure sharing and compare them in terms of security, scalability, maturity and convenience.