Hong Linh Truong

A dynamic link adaptation algorithm for IEEE 802.11 a wireless LANs

We present a simple but powerful dynamic link adaptation mechanism for wireless LANs, which are based on the IEEE 802.11a standard. Using this method, a transmitter is able to detect whether the quality of the link is improving or deteriorating, and based on this information to switch to a higher or lower transmission rate, respectively. For determining the link quality, the transmitter employs only information that is available locally. Therefore, the proposed method can be implemented without changes or enhancements to the current IEEE 802.11 standard. The efficiency of our method is investigated and evaluated by means of simulations.

Dynamic Data Rate and Transmit Power Adjustment in IEEE 802.11 Wireless LANs

In this paper a novel link adaptation algorithm is proposed that is capable of adjusting the transmit power level and the data rate jointly to the radio channel conditions. The proposed method relies solely on link quality information available at the transmitter by employing the reception or non-reception of the acknowledgment frames as a measure of the channel quality with respect to the power level and data rate. The method is fully compatible with the 802.11 wireless LAN standard. In contrast to many other proposals, it neither relies on the RTS/CTS protocol nor requires a feedback channel to transmit link-quality estimates from the receiver to the transmitter. Different strategies for optimizing the data rate and power level are given. These depend on the scenarios considered, the number of active stations, and the service requirements. The two main strategies are either to drive the system towards the highest possible data rate and adjust the rate and power levels accordingly (“high-performance” mode) or to focus on power saving, possibly trading this for other performance criteria such as throughput or delay performance (“low-power” mode). Other special cases, such as power or rate only adaptation, are also discussed. It can be shown that in most cases the best choice for achieving low transfer times, maximizing throughput, and alleviating the hidden terminal problem is to transmit at the highest possible rates and with high power levels. This “high-performance” mode of operation also minimizes the transmission times, which in turn maximizes the time for putting idling components into a sleep mode, thereby minimizing the overall power consumption.

Power and rate adaptation in IEEE 802.11a wireless LANs

We present a simple but powerful dynamic link adaptation mechanism for wireless LANs that is compliant with the IEEE 802.11a standard. Using this method, a transmitter is able to estimate the current link quality and, based on this information, to adapt the transmission parameters, namely the transmission data rate or the transmission power level, dynamically. To determine the link quality, the transmitter employs only information that is available locally. Therefore, the proposed method can be implemented without changes or enhancements to the current IEEE 802.11 standard. The efficiency of our method is investigated and evaluated by means of simulations.

Flight of the FALCON (ATM)

The fabric-based ATM oriented local connectivity (FALCON), an ATM-based customer premises network (CPN), is described. FALCON supports access using traditional local area networks (LANs) such as Ethernet and token rings and supports a LAN emulation mode for its native ATM interface. This service allows a set of terminals, workstations, and servers to connect to the switch-based network and to interact as if they were attached to a traditional LAN. FALCONs backbone structure is based exclusively on ATM technology, all following CCITT or industry standards wherever they apply. The FALCON control structure is outlined.<<ETX>>

Performance evaluation of the QoS enhanced IEEE 802.11e MAC layer

Much research work is currently focusing on the optimization of the MAC performance of high data-rate next generation wireless local area networks (WLANs). In particular, the IEEE 802.11 task group E is working on a draft proposal for a QoS-aware MAC protocol for the most widespread WLAN technology. This draft considers several service differentiation mechanisms, based on both contention and polling schemes, whose effectiveness is still under investigation by the task group. In this paper, we study the performance of this 802.11e MAC protocol by means of computer simulations in which the specifications given in the draft have been implemented in great detail. Real-life scenarios, such as home networking and hot spot environments, are considered to evaluate the effectiveness of the various 802.11e QoS mechanisms in supporting voice, video and data applications.

A power-efficient wireless sensor network for continuously monitoring seismic vibrations

We present a novel power-efficient wireless sensor network for continuously monitoring and analyzing seismic vibrations with sensor nodes and forwarding the retrieved information with low-cost relay nodes to backend applications. The applied vibration sensing algorithms are derived from the DIN 4150–3 standard. All nodes in the network are battery-powered and equipped with an IEEE 802.15.4 compatible radio transceiver. The nodes communicate with each other by executing a novel power-efficient protocol stack, which provides all network functions required by the vibration-sensing application and uses a publish/subscribe messaging protocol for communicating between the network nodes and the backend applications. Results obtained in certification and field tests show that the proposed vibration-sensing solution is standard-compliant, and that the wireless vibration sensor network (WVSN) exhibits excellent performance in terms of packet delivery rate, latency, and power efficiency.

ATM direct connectionless service

A method is proposed by which an asynchronous transfer mode (ATM) network can directly provide a connectionless data service in a customer premises network. Cells that carry connectionless messages are routed to their destination based on an address written in the VPI/VCI field. This is performed directly by the ATM switches, without any overlay switching functions. The method applies to one addressing domain, which can match a customer premises network. The basic protocols and a buffer protection scheme which can be employed for implementing the service are given. For destinations outside the domain, the protocols allow a transparent use of the connectionless service defined by the CCITT.<<ETX>>

A multiMAC approach to overcome the throughput limits of 802.11 WLANs

In this paper, we explore MAC approaches that could provide increased throughput to 802.11 WLANs. First we analyze the throughput performance of 802.11 WLANs by deriving expressions for the maximum achievable throughput. Based on these results, we identify the main throughput-limiting factors and discuss approaches that may reduce their impact. We also propose a novel approach, called multiMAC, which allows a significant throughput increase without the need for new high-rate transmission modes. An important feature of our approach is its interoperability and compatibility with current 802.11 WLANs. Furthermore it is very simple, requires no hardware support, and can easily be implemented in software.

Wireless sensor network for continuous temperature monitoring in air-cooled data centers: applications and measurement results

Temperature monitoring in data centers is essential for reliably operating the data processing equipment and minimizing the required cooling energy. For this purpose, we track the temperatures at key locations in the data center with low-cost sensors and forward the captured information via the ZRL Data Center Wireless Sensor Network (DCWSN) to a monitoring client. Applications include continuous temperature monitoring, data collection for thermal modeling, and temperature sensing for real-time control of cold air flow and workload allocation. The DCWSN has been successfully deployed in production data centers.