Evgeny M. Khorov

A survey on IEEE 802.11ah

We study carefully the IEEE 802.11ah draft standard published in July 2014.We overview use cases of .11ah, especially related to smart cities scenarios.We describe in details novel mechanisms and explain why they are needed in .11ah. Smart technologies play a key role in sustainable economic growth. They transform houses, offices, factories, and even cities into autonomic, self-controlled systems acting often without human intervention and thus sparing people routine connected with information collecting and processing. The paper gives an overview of a novel Wi-Fi technology, currently under development, which aims to organize communication between various devices used in such applications as smart grids, smart meters, smart houses, smart healthcare systems, smart industry, etc.

Flexibility of Routing Framework Architecture in IEEE 802.11s Mesh Networks

The fundamental challenges in wireless multihop networks design are the problems of routing and hidden stations. Defining mesh networking, IEEE 802.11s amendment addresses both issues. It includes a routing protocol and novel deterministic channel access method, called MCCA, complementing random access traditional in IEEE 802.11 networks. The routing framework architecture allows extending or even replacing the default routing protocol for specific niche application, but it is not flexible enough to take advantage of using both traditional random access and novel deterministic access, as we show in this paper. Proposed flexibility enhancements are illustrated to bring benefits for the network performance.

Real-Time Station Grouping under Dynamic Traffic for IEEE 802.11ah

IEEE 802.11ah, marketed as Wi-Fi HaLow, extends Wi-Fi to the sub-1 GHz spectrum. Through a number of physical layer (PHY) and media access control (MAC) optimizations, it aims to bring greatly increased range, energy-efficiency, and scalability. This makes 802.11ah the perfect candidate for providing connectivity to Internet of Things (IoT) devices. One of these new features, referred to as the Restricted Access Window (RAW), focuses on improving scalability in highly dense deployments. RAW divides stations into groups and reduces contention and collisions by only allowing channel access to one group at a time. However, the standard does not dictate how to determine the optimal RAW grouping parameters. The optimal parameters depend on the current network conditions, and it has been shown that incorrect configuration severely impacts throughput, latency and energy efficiency. In this paper, we propose a traffic-adaptive RAW optimization algorithm (TAROA) to adapt the RAW parameters in real time based on the current traffic conditions, optimized for sensor networks in which each sensor transmits packets with a certain (predictable) frequency and may change the transmission frequency over time. The TAROA algorithm is executed at each target beacon transmission time (TBTT), and it first estimates the packet transmission interval of each station only based on packet transmission information obtained by access point (AP) during the last beacon interval. Then, TAROA determines the RAW parameters and assigns stations to RAW slots based on this estimated transmission frequency. The simulation results show that, compared to enhanced distributed channel access/distributed coordination function (EDCA/DCF), the TAROA algorithm can highly improve the performance of IEEE 802.11ah dense networks in terms of throughput, especially when hidden nodes exist, although it does not always achieve better latency performance. This paper contributes with a practical approach to optimizing RAW grouping under dynamic traffic in real time, which is a major leap towards applying RAW mechanism in real-life IoT networks.

QoS support for bursty traffic in noisy channel via periodic reservations

The growth of the number of devices working at the same area, overlapping networks and multihop data transmission degrade the efficiency of contention based channel access. A number of deterministic channel access methods introduced in recent Wi-Fi standards allow to reserve a set of periodical time intervals, during which a single station can access channel without contention. Providing collision free transmission, these methods are favourable for real-time multimedia traffic which demands high quality of service (QoS). However, QoS provisioning for multimedia transmission is significantly complicated by the bursty nature of multimedia traffic and random noise inherent to wireless channels. In this paper, we propose an analytical model of multimedia transmission via periodic reservations considering both multimedia traffic bursty nature and random noise. The model can be used to find reservation parameters which allow to meet QoS requirements while transmitting multimedia data.

Several EDCA parameter sets for improving channel access in IEEE 802.11ax networks.

To improve efficiency of wide channel usage in dense scenarios, Wi-Fi community is currently developing a new amendment - 802.11ax - which introduces OFDMA in Wi-Fi. To provide backward compatibility, OFDMA works on top of CSMA/CA, native for Wi-Fi. Although OFDMA transmission is much more efficient than traditional one, the straightforward usage of 802.11ax functionality leads to the low ratio of OFDMA uplink transmissions. This problem can be solved by changing channel access parameters, which can be done with a legacy mechanism. However, in a heterogeneous network with legacy and 802.11ax stations, this mechanism leads to severe unfairness. In the paper, we describe our recent proposal, which solves the problem, and evaluate its performance with an analytical model.

Analytical study of link management in IEEE 802.11s mesh networks

Efficient link management is important for mesh networking. The links opened between neighbor STAs should be stable and ensure high probability of packet delivery. Various approaches of link management are usually compared by simulation. The core contribution of this paper is original link management efficiency criteria and an analytical model of decision-making process of link management in IEEE 802.11s, which are used to improve network performance.

QoS-aware streaming with HCCA TXOP negotiation in overlapped Wi-Fi networks

To avoid collisions in Wi-Fi networks, access points (APs) - acting as coordinators - got the ability to use centralized contention-free channel access, e.g. HCCA, which supports parameterized QoS. However, the growth of WLANs population raises a problem of coordination between APs. As a solution to this problem, IEEE 802.11aa introduces the HCCA TXOP Negotiation mechanism, which allows APs to agree in advance on periodic time intervals used by each AP for contentionfree channel access. The paper studies the efficiency of such a mechanism, focusing on developing a model, which allows selecting appropriate reservation parameters to minimize channel resource consumption while transmitting several flows with given QoS requirements1.

Study of the group-based approach to disseminate control information in wireless networks

Various networking protocols disseminate much control information. An important task is to reduce the amount of such information in order to free channel resources for user data. In the paper, we study a novel group-based approach for dissemination of control information introduced in the latest version of the IEEE 802.11 standard. The key idea of this approach is to join various pieces of information into a small number of groups and send differential updates related only to those groups which content is changed. However, the group management algorithm (GMA) which directly affects the performance of such an approach is not specified. We consider a simple GMA, develop an analytical model to estimate the amount of sent control information, and show that this amount is significantly less than for the classical full dump approach.

Will MCCA revive wireless multihop networks

Wireless multihop networks (WMNs) are very favorable for many emerging applications, including those connected with public safety, Internet of Things or future Next Generation 60 GHz communication. However, the hidden station problem dramatically degrades efficiency of WMNs and impedes extensive usage of these networks. To eliminate the effect of hidden stations in Wi-Fi mesh networks, the latest version of the IEEE 802.11 standard proposes using deterministic channel access called MCCA. In the paper, we analyze this mechanism, focusing on both already achieved results and open issues.

Analytical Model of QoS-Aware Streaming in Wi-Fi Networks via Periodic TXOPs

To improve Wi-Fi performance in scenarios with high collision probability, recent amendments to the Wi- Fi standard introduce a number of channel access methods based on preliminary channel time reservations. A common feature of these methods is that channel time is reserved in a periodic manner. Unfortunately, having defined a number of channel reservation methods, the amendments say nothing on how much channel time shall be reserved to transmit a stream with required quality of service and minimal channel resource consumption. In this paper, we develop a mathematical model of streaming via periodic reservations which helps to answer this question.