The broadcast nature of a wireless link provides a natural eavesdropping and intervention capability to an adversary. Thus, securing a wireless link is essential to the security of a wireless network, and key generation algorithms are necessary for securing wireless links. However, traditional key agreement algorithms can be very costly in many settings, e.g. in wireless ad-hoc networks, since they consume scarce resources such as bandwidth and battery power.Traditional key agreement algorithms are not suitable for wireless ad-hoc networks since they consume scarce resources such as bandwidth and battery power. This paper presents a novel approach that couples the physical layer characteristics of wireless networks with key generation algorithms. It is based on the wireless communication phenomenon known as the principle of reciprocity which states that in the absence of interference both transmitter and receiver experience the same signal envelope. The key-observation here is that the signal envelope information can provide to the two transceivers two correlated random sources that provide sufficient amounts of entropy which can be used to extract a cryptographic key. In contrast, it is virtually impossible for a third party, which is not located at one of the transceiver's position, to obtain or * This work was done in part while the author was with Rensselaer Polytechnic Institute.Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. predict the exact envelope; thus retrieve the key. Since in the presence of interference strict reciprocity property can not be maintained; our methodology is based on detecting deep fades to extract correlated bitstrings. In particular, we show how a pair of transceivers can reconcile such bitstrings and finally flatten their distribution to reach key agreement. In our constructions we use cryptographic tools related to randomness extraction and information reconciliation. We introduce "secure fuzzy information reconciliators" a tool that enables us to describe robust key generation systems in our setting. Finally we provide a computational study that presents a simulation of a wireless channel that demonstrates the feasibility of our approach and justifies the assumptions made in our analysis.

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Abstract-This paper addresses the problem of adaptive quality-of-service (QoS) for mobile multimedia services under a power controlled wireless network using smart antennas. Given the nature of multimedia, we chose the signal-to-interference and noise ratio (SINR) of each user's channel as the QoS index. We direct our attention toward two problems. The first is to increase the SINR levels for multimedia users as much as the system can provide for, under the channel fading and interference conditions. Different users have distinct desired SINR levels according to their requested service types; our algorithm uses an iterative method to drive the SINR levels as close as possible to those desired levels. The SINR levels are improved without deteriorating quality for other types of users. Simulations presented here show a significant increase in the average SINR levels for multimedia users. The second problem considered in this paper, is how to speedily initiate new users into the network by using lower complexity algorithms that yield reliable results. As shown in the simulations, our fast activation scheme can substantially reduce the time for activating new users into the system.

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Absfrucf-A wireless network that provides multimedia services should control the quality of the transmission link for users, allocating resources according to the service type of each user, be it voice, video, image or data. This paper proposes a scheme to allocate the desired signal to interference noise ratio (SINR) for those users with multimedia services by exploiting power control and smart antennas, while not affecting users with voice service. A method to quickly initialize new users into such a network is also proposed.

programmes. Furthermore, the value of having clinical teaching staff with a fixed teaching remit was evident. The results of the study were useful to inform detailed planning of rotations and allocation of teaching resources. Context and setting Medical students invest a significant amount of time studying human structure using a variety of resources. They often find it challenging to visualise the functioning living human and to apply their learning clinically. Because ultrasound imaging provides a means of visualising structure and movement in a living person, it was proposed that it could be used to enhance and facilitate the learning of functional clinical anatomy. An ultrasound learning resource was located within the anatomy area to enable students to integrate their learning through ultrasound with the study of specimens and other resources. Why the idea was necessary The purpose of the study was to determine the effect on student learning of integrated ultrasound anatomy teaching sessions. These sessions included an introduction to the technology of ultrasound imaging and the hands-on experience of performing an examination in order to provide students with the opportunity to develop basic imaging skills, and to enhance their knowledge of surface and visceral anatomy. What was done Groups of 6 first-year medical students had an integrated clinical skills, anatomy and radiology session, followed by a series of 3 90-minute ultrasound anatomy sessions provided by a radiologist during the cardiovascular and renal subunits. The sessions included an introduction to the use of the ultrasound imaging, the setting of learning objectives, guidance on the location of landmarks and the visualisation of organs and tissues, a handson experience conducting an ultrasound examination on a living human, a discussion of its clinical relevance and an evaluation of the session. The objectives of the examinations were to use various approaches and scans to visualise and identify specific cardiac structures, major abdominal vessels, carotid arteries and the kidneys, as well as noting the relationships of adjacent structures. Videos of related pathologies were also discussed.The students were evaluated on their ability to perform an ultrasound examination at the end of the first and the last sessions, and received formative evaluation. For this study, a 5-point scale was used: from 1 ¼ poor (inadequate identification of 'acoustic window' required for visualisation of prioritised structures) to 5 ¼ excellent (ability to detect normal and pathological surface anatomy and functional morphology on reference standards). Approximately 490 medical students from 4 consecutive classes participated.The average score at the end of the first session was 3.25 ± 0.12, compared to the last session (4.15 ± 0.16; P < 0.005). The scores from this study were not provided to the students or incorporated into their formal evaluation. The student evaluations of the sessions were consistently excellent (score of 5 ⁄ 5), and included highly positive c...

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