IEEE 802.11ah is a new wireless LAN technology proposed mainly for IoT (Internet of Things). Operating at frequency band under 1 GHz, 802.11ah WLAN can provide much extended coverage range and support around 8,000 nodes to be associated with a single AP. Such a dense environment may cause hidden terminal problems which can severely degrade the performance of the network. Thus, the 802.11ah standard adopts a group based MAC protocol such that the nodes are divided randomly into several groups and members of a group contend to access channel within their allocated RAWs (Restricted Access Windows). However, the random grouping method cannot solve the hidden terminal problem sufficiently. In this paper, we propose a novel grouping mechanism that groups the nodes by their hidden-terminal relationship: i.e., any two nodes hidden to each other are assigned to different groups, and thus access the channel using different RAWs. Mathematic analysis and simulations show that our proposed scheme remarkably improve the performance of Sub-1 GHz WLAN.

IEEE 802.11p has adopted DCF (distributed coordination function) for multiple access in vehicular ad-hoc networks. In broadcasting, however, the 802.11p standard cannot provide reliable transmissions, since the receivers do not send any feedbacks. In this paper, in order to make 802.11p more reliable, we propose a BCs (backoff counters) reservation scheme with collision detection: vehicles can reserve their BCs by observing idle channels, such that collisions due to identically chosen BCs can be avoided; an algorithm to determine the BC values is given, which enables transmitter to detect transmission collisions by providing implicit feedbacks. Using simulations, we show our proposed backoff mechanism can remarkably improve the performance of 802.11p vehicular networks.

IEEE 802.15.4 low-rate WPAN defines GTS (Guaranteed Time Slot) allocation based on FCFS (First Come First Serve) basis. In case of an emergency traffic, however, it may be hard to receive time slots because of other traffic flows already in service. In this paper we propose an efficient way of allocating GTS to emergency data so that the emergency traffic can get time slots whenever they request. Traffic with a higher data rate is preferred. Extensive simulation results show that our proposed scheme gives a guaranteed GTS allocation to urgent nodes and also enhances overall throughput.

Both of high-rate and low-rate wireless personal area networks (WPANs), being under development by several standardization bodies, are considering to adopt distributed TDMA MAC protocols in order to provide seamless user mobility for WPAN mesh as well as a good peer-to-peer QoS. It has been, however, pointed out that the absence of a central controller in the wireless TDMA MAC may cause a severe performance degradation: e.g., fair allocation, service differentiation, and admission control may be hard to achieve or can not be provided. In this paper, we suggest a new framework of resource allocation for the distributed MAC protocols in WPANs. Simulation results show that our algorithm achieves both a fair resource allocation and flexible service differentiations in a fully distributed way for mesh WPANs where the devices have high mobility and various requirements. We also provide an analytical modeling to discuss about its unique equilibrium and to compute the lengths of reserved time slots at the stable point.

The emerging high-rate wireless personal area network (WPAN) technology, currently being developed by IEEE 801.15.3 task group, provides a very high-speed short-range transmission capability with quality of service provisions. MPEG-4 bit stream is anticipated to occupy a large portion of the traffic in the WPAN, and its decoding depends on successful transmissions of frame data, which require a low JFR (job failure rate) and a Iow delay variance as well as a high throughput. In this paper, we propose a simple application-aware MAC scheme for the WPAN in order to achieve a high-quality video transmission of MPEG-4 stream: a device tells the piconet controller the maximum sizes of its frames along with the channel time requests, and then the controller allocates a channel time for the device according to the predefined MPEG frame sequence. Simulation results show that our scheme achieves significantly lower JFRs, lower delay variances, and higher throughputs than the standard scheduling scheme.

We investigate the problem of virtual path (VP) capacity allocation in a decentralized way. Users (VP controllers), sharing common network resources, are assumed to control their VP capacities according to their performance measures. We formulate a model that differs from previous ones in two points: first, each user has its own performance objective that is simply assumed to be concave and smooth; second, a user's strategy (VP bandwidth reservation) is constrained between two numbers. Adopting a standard game-theoretic formulation, we prove that there exists a unique network operating point-Nash equilibrium. We show several interesting properties of the equilibrium and also look at the convergence of some distributed algorithms. After studying the combined problem of routing and flow control in parallel link networks, we investigate the problem of VP capacity allocation in general topology networks, where fixed routing is assumed. Finally, examples of the model are presented.