Spatial coordinated medium sharing: Optimal access control management in drive-thru internet

Driven by the ever-growing expectation of ubiquitous connectivity and the widespread adoption of IEEE 802.11 networks, it is not only highly demanded but also entirely possible for in-motion vehicles to establish convenient Internet access to roadside WiFi access points (APs) than ever before, which is referred to as Drive-Thru Internet. The performance of Drive-Thru Internet, however, would suffer from the high vehicle mobility, severe channel contentions, and instinct issues of the IEEE 802.11 MAC as it was originally designed for static scenarios. As an effort to address these problems, in this paper, we develop a unified analytical framework to evaluate the performance of Drive-Thru Internet, which can accommodate various vehicular traffic flow states, and to be compatible with IEEE 802.11a/b/g networks with a distributed coordination function (DCF). We first develop the mathematical analysis to evaluate the mean saturated throughput of vehicles and the transmitted data volume of a vehicle per drive-thru. We show that the throughput performance of Drive-Thru Internet can be enhanced by selecting an optimal transmission region within an AP's coverage for the coordinated medium sharing of all vehicles. We then develop a spatial access control management approach accordingly, which ensures the airtime fairness for medium sharing and boosts the throughput performance of Drive-Thru Internet in a practical, efficient, and distributed manner. Simulation results show that our optimal access control management approach can efficiently work in IEEE 802.11b and 802.11g networks. The maximal transmitted data volume per drive-thru can be enhanced by 113.1% and 59.5% for IEEE 802.11b and IEEE 802.11g networks with a DCF, respectively, compared with the normal IEEE 802.11 medium access with a DCF.

Procedural learning in children with developmental coordination disorder

Despite the fact that developmental coordination disorder (DCD) is characterised by a deficit in the ability to learn or automate motor skills, few studies have examined motor learning over repeated trials. In this study we examined procedural learning in a group of 10 children with DCD (aged 8–12 years) and age-matched controls without DCD. The learning task was modelled on that of Nissen and Bullemer [Cognitive Psychology 19 (1987) 1]. Children performed a serial reaction time (SRT) task in which they were required to learn a spatial sequence that repeated itself every 10 trials. Children were not aware of the repetition. Spatial targets were four (horizontal) locations presented on a computer monitor. Children responded using four response keys with the same horizontal mapping as the stimulus. They were tested over five blocks of 100 trials each. The first four blocks presented the same repeating sequence, while the fifth block was randomised. Procedural learning was indexed by the slope of the regression of RT on blocks 1–4. Results showed that most children displayed strong procedural learning of the sequence, despite having no explicit knowledge about it. Overall, there was no group difference in the magnitude of learning over blocks of trials – most children performed within the normal range. Procedural learning for simple sequential movements appears to be intact in children with DCD. This suggests that cortico-striatal circuits that are strongly implicated in the sequencing of simple movements appear to be function normally in DCD.