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— We analyze the performance of the IEEE 802.11b wireless local area networks. We have observed that when some mobile hosts use a lower bit rate than the others, the performance of all hosts is considerably degraded. Such a situation is a common case in wireless local area networks in which a host far away from an Access Point is subject to important signal(More)
We consider wireless LANs such as IEEE 802.11 operating in the unlicensed radio spectrum. While their nominal bit rates have increased considerably, the MAC layer remains practically unchanged despite much research effort spent on improving its performance. We observe that most proposals for tuning the access method focus on a single aspect and disregard(More)
— We analyze in this paper the fairness of the 802.11 DCF (Distributed Coordination Function) access method. Short-term fairness is an important property of a MAC layer for obtaining short delays. We show that contrary to the common wisdom, a 802.11 cell with two hosts does not exhibit short-term unfairness. Many papers considered 802.11 as short-term(More)
Previously, we have analyzed the short-term fairness of the 802.11 DCF (Distributed Coordination Function) access method in the case of a network with two hosts. In this paper we extend the analysis to an increased number of hosts. We use two fairness indices. The first one is the number of inter-transmissions that other hosts may perform between two(More)
An overwhelming part of research work on wireless networks validates new concepts or protocols with simulation or analytical modeling. Unlike this approach, we present our experience with implementing the <i>Idle Sense</i> access method on programmable off-the-shelf hardware---the Intel IPW2915/abg chipset. We also present measurements and performance(More)
In atypical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as abridge between the wireless and the wired parts of the network. Under the current IEEE 802.11 Distributed Coordination Function (DCF) access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay(More)
Many researchers have addressed the problem of QoS differentiation in 802.11 wireless networks, however no method proposed so far benefits from all desirable properties: high aggregate throughput even for a large number of contending stations, fair allocation to all stations in the same class, fast adaptation to changing conditions, and support for absolute(More)
IEEE 802.15.4 defines a popular MAC standard for wireless sensor and actuator networks. With the default parameters, under medium to high load, 802.15.4 generates excessive collisions and packet losses. Low duty cycles even exacerbate the problem, because more nodes become active after long periods of sleep and contend for channel access. In this paper, we(More)
— MAC protocols based on preamble sampling techniques like WiseMAC and BMAC offer significant energy savings for multihop wireless sensor networks. Although preamble sampling based techniques efficiently reduce idle listening in low-rate data networks, they introduce extra overhead due to possible reception of some irrelevant frames. In this paper, we(More)
We propose a new access method for wireless multi-hop sensor networks. It reduces collisions due to hidden nodes, a source of significant energy dissipation. Our access method operates similarly to SMAC by alternating sleeping and active periods, but it does not use RTS/CTS. Instead, it adjusts the contention window so that the probability of collisions due(More)